I have both 75 with automatic transmission. The snow button, what it does is it locks the overdrive. This makes it go slower from a standstill so you won't lose the initial traction needed to start moving on the snow. So it's also correct what they have indicated about stepping on the brake on downhill slopes to "activate" the engine braking, making the gearbox move from a previous high gear to the previous one.
Cheers...!!!