Traction control modulates power to the wheels if they start to spin. This makes it much easier to drive and control even a rear-wheel-drive car in snow.
Traction control doesn't help with turning or stopping a car, but it can help to get a car moving on a slippery surface. It can also help avoid accidents caused by cars losing control due to too-quick acceleration on slippery roads or sliding too slowly into an intersection ahead of on-coming cars instead of driving through.