(FORTUNE Magazine) – The headline happened to appear in the St. Louis Post-Dispatch recently, but you hear the sentiment everywhere: WALL STREET'S MERGER MANIA AFFECTS MANY ON MAIN STREET; SHAREHOLDERS WIN, BUT WORKERS MAY PAY THE PRICE. The lead of the story, I must say, was unusually loaded with the language of proletariat vs. robber barons: "As janitors sweep up the last of the champagne corks in executive boardrooms around the world, now may be a good time to examine what the latest wave of corporate mergers means for the rest of us." You can just imagine. At least in this view, the meaning is very grim.

Okay, it's upsetting to see your industry getting turned inside out by deal-besotted CEOs who may suffer from hormone imbalances, and nothing can change that. But it's time to correct the conventional wisdom that these deals are driven by potential economies based on mass layoffs. The startling reality is that most takeovers have never been about saving money by firing people, and that's truer than ever today, when the whole point of many acquisitions is getting people. What most takeovers are about is making companies bigger and stronger fast, when the planets align to make that possible in this especially dramatic way. And isn't a fast-growing company where you want to be?

Now excuse me for a moment while I try to forestall some mail. A few lines back I said "most takeovers"--not all. In some deals, including some high-profile ones in banking particularly, layoffs are definitely part of the rationale from the day the deal is conceived. We'll get to these shortly. The trouble is that they attract disproportionate attention, skewing a lot of employees' view of the mergers and acquisitions phenomenon and creating needless anxiety.

So what really drives a takeover wave, like the historically massive one roaring all around us? Ask 100 people, and I'm pretty confident at least 90 will say something about economies of scale. What could be more obvious--isn't that one of the main advantages of being bigger? Maybe, but the people who study these things have a hard time showing that it has much to do with why firms merge. In fact, many researchers don't believe it's a significant factor. Consider: If companies merged because they needed to save money, you'd expect takeovers to increase during economic contractions, when cost pressures are heaviest. What actually happens is just the opposite--M&A goes crazy when the economy booms. To take the largest example available, is Travelers buying Citicorp to save money? Of course not: The whole point is to increase revenues significantly through cross-selling (a strategy that certainly remains to be proven).

The actual causes of takeover waves seem to be even more elemental than cost savings. An academic study of the great consolidation of the '90s cites as main factors "the generally favorable conditions of business" combined with "a rising, buoyant securities market" at a time of "too much productive capacity." Just one thing: This was a study of the merger wave of the 1890s, not the 1990s (Merger Movements in American Industry 1895-1956 by Ralph L. Nelson, published in 1959). What's striking is how true this analysis rings today. That century-ago burst of M&A, like today's, featured not much vertical integration but a whole lot of horizontal takeovers in which several industries consolidated into a few giant companies each. And it happened because conditions in the capital markets enabled CEOs to do what they've always wanted to do and always will: eliminate competitors, get control of more capacity, try to gain a little market power, and grow.

Not that the causes remain even as rational as that. Once a deal boom starts, frenzy takes over as the predominant force. Those who work on these deals every day harbor no doubt that they're happening fast because they're happening fast: You'd better make your deal now before your competitor steals it.

Amid this turmoil, you're right if you suspect that your career is at the top of no one's mind but your own. And undoubtedly some CEOs who weren't thinking about layoffs when they made their latest deals will find on sobering up that they overpaid and must cut costs, which they'll accomplish partly by firing people. But there are reasons the largest M&A wave in America's history is coinciding with the lowest unemployment rate in a generation, reasons that should make most people glad to see this wave roll on.

The very root of many of today's takeovers is that the acquiring company desperately needs people, and buying a company is the fastest way to get them. In an economy based increasingly on intellectual capital, a company's assets are in employees' heads; no employees, no assets, no deal. You see this especially in pure-intellect industries like infotech, biotech, and consulting. Cisco Systems, for example, makes lots of acquisitions solely to get the target company's employees. Compensation consultants are being forced to devise ever more effective golden handcuffs, a development we all should applaud.

Many of the latest takeovers, affecting hundreds of thousands of workers, are not the giant deals that make the papers but much smaller ones, parts of industry roll-ups that span the economy. Florists and funeral homes have been rolled up, car dealers and building-maintenance firms are being rolled up, and the trend has far to run. Here, too, keeping local managers is often crucial to success. Lower costs are an important reason for roll-ups, but they come mainly from savings in purchasing, not layoffs.

And overlaying the whole M&A phenomenon is the central fact that it's primarily about making the top line larger. Look at any list of the biggest recent deals--they're mainly intended to increase geographic reach (SBC-Ameritech), fill out a product line (Dean Witter-Morgan Stanley), or respond to deregulation (American Electric Power-Central & Southwest). The outstanding exceptions, where savings through layoffs are an obvious major attraction, are in banking. Many thousands have been fired as this industry consolidates, and thousands more will be.

Yet even if the worst happens and you do lose your job, the surging economy that's prompting the merger wave is also creating new jobs at a scorching pace. Listen to Robert Reich, Bill Clinton's former Labor Secretary, the man whose mission was to keep Americans employed, cheerleading for the M&A boom in a recent op-ed article: "Some employees will lose their jobs, of course. But that's less of a problem now, when fewer than 5% of workers across the nation are actively looking for jobs. Digital is expected to cut some 15,000 jobs, or 28% of its present work force, after merging with Compaq. Yet almost all those jobs are in Massachusetts, where unemployment is down to 3.7% and where other high-tech companies are recruiting like mad."

Yes, sometimes mergers do lead to layoffs. If that makes you wonder which way your industry is headed, answering a couple of questions should make the picture clearer.

How is your industry shaking out? Wharton professor George S. Day distinguishes between "boom and bust" shakeouts and "seismic-shift" shakeouts. In the first kind, a fundamentally new business entices dozens of startups, only a few of which can survive. That was the auto industry 90 years ago, and it is, for example, the Internet-related businesses of today. This isn't a bad place for an employee to be. Your firm may not survive, but if you're a good worker, you stand an excellent chance of participating in the industry's rapid growth. (If you're not a good worker, which industry you're in doesn't much matter.) Seismic-shift shakeouts aren't so reassuring. Those are cases in which some big development--deregulation, a technological breakthrough--fundamentally changes the game. Banking is going through one of them (a double one, in fact, sparked by deregulation and the Web), resulting in a new model of the industry that requires fewer people. This is often the case with seismic-shift shakeouts.

What kind of worker are you--a brain or a bureaucrat? That's an oversimplification, and it's a disservice to many bureaucrats, but you know what I mean. Even in industries laying off thousands, some people keep their jobs. Who stays and who goes has much to do with this question. Think of it this way: Does your work require your creative intelligence every day? Or this way: In five years, is it possible that a computer could do your job, or a large part of it? If your work doesn't demand that you perform essentially, exclusively human tasks--creating, judging, imagining, building personal relationships--then you're at grave risk in the inevitable post-takeover scrutiny of who's doing what around the company.

Having sounded the warnings, I emphasize the bottom line: Now just ain't the time to worry about larger economic forces hurting your career. As the merger wave continues, be of good cheer; it's happening only because the economy is vibrant, stocks are high, and companies are determined to grow. They need you. When merger mania finally cools down--start worrying.