I haven't missed a day commuting to work since July 2006. In part, it's due to studs. They take all the worry out of icy surfaces. (Note that in the photo above, studs, or even snow tires, weren't necessary that day since the snow was so gushy it just squoze out from under the tires.)

No matter how many tons of salt the DPW throws down, there's always a few strategically placed patches of ice that get missed. And side streets are never salted here, so in the course of a Great Lakes winter, hardpack turns to ice, a warm day melts it a bit, then a cold night re-freezes it to icy ruts. Studs can get me through.

Two things to keep in mind: First, studs help only on ice. They don't do a thing for you in snow or hardpack. Helpfully, studs come attached to winter tires that do help in those cases. But if your cycling is only occasional, and only in snow without any ice, you can get by without them.

Second, the purpose of studs on a two-wheeled vehicle is different than on a four-wheeled one. They're not there to help you get going--although they help with that. They're there to keep the wheels from sliding out sideways from beneath you.

As for their efficacy on ice, I've ridden on surfaces that I can't stand on--let alone walk--and where cars just slide sideways. I have plenty of stories about riding around cars, trucks, even buses that just spin, spin, spin, and riding past pedestrians walking like penguins.

Now, if your cycling is off-road, and you're not riding across ponds, they may not be necessary at all. Off-road isn't my thing in any weather, so I can't say.