I did clipless this winter. I think it does help sometimes when you need the control to power through some sloppy slippery stuff at low speed, or take a tight corner at a crawl. Releasing in time to put a foot down is never an issue.

Winter biking and mountain biking have a lot in common. The first time I rode clipless on a mountain bike ride, I was apprehensive about the idea (I was comfortable with clipless, but new to mountain biking). I figured, though, that a slow-speed tip-over with the clipless was better than getting rattled off the platform pedals at higher speeds. I had to do a LOT of emergency foot dabbing in some of the tight switchback climbs (I'm not very talented in tight spots), and every time I saved myself from tipping over, I was kind of amazed. I didn't even have to think about it... and my foot was free. That sideways heel twist really does become your natural reaction after a while! Now I've even gone winter mountain biking with clipless, and it truly does give you the extra bit of power and control when you really need it.