I bought a brand new 2000 BMW 323i in the spring, so I never really figured out what the traction control would do. It reduced power to one or both rear wheels if it sensed a loss of traction, rather than let the wheel spin.
So after the first messy slippery snow of the season, I turned into my driveway. Halfway up the small rise, the car simply stopped dead. I pushed on the accelerator, but it sat there, no response from the engine. So I turned off traction control, and it immediately slid backward down the hill.