Me and my buddy both lost are footing the first day riding a 850. I like it coming down chutes and steep area's just anticipate it. I had a problem with my machine getting away and the 850 don't go as far as my rmk.
Joe pretty much nailed it...many factors go into engine/clutch braking. Another would be snow conditions!
To eliminate engine braking when descending (if you desire), just lock the track up for a second when going slow....this will allow the primary to disengage and you will have nothing but drivetrain drag. To get it back just tickle the throttle to engage the primary clutch.