Can they also be used on clean roads? I've never seen them, but roads are mostly clean again within a few days after snowfall.
We did see some off-the-road cyclists last week with mud on their backs up to their hair and even in their faces. I had problems envisioning these people considering that as fun.
Yes, there's no problem at all with them when the roads are clean and dry - that's the case here for most of my winter rides. They have a little bit more rolling resistance than summer tyres, and they have their own special rolling sound, but that's all. (If you go fast enough, you might not have to ring your bell to get the pedestrians out of the way... they will hear you coming.)
So I (or we) ride a little less fast in winter, but being and feeling safe on icy spots when and where they do happen more than makes up for that.