I often wear my compression socks while riding. I've got various ones, from ones that only cover half my foot and go up to the end of my calves and look like pantyhose-type material and are meant to be worn under something else, up to full-coverage socks that go from the toes up to nearly my knees, and can be worn alone as normal socks.

I've got circulation issues from varicose veins in my legs that make this a good idea. I don't always wear them, but I should, and if I don't and sit down all day at my computer I'll often notice some swelling in my feet and ankles by the end of the day. If I wear them I don't. The nearly knee-high ones aren't as comfortable to wear as just normal socks, but for a long ride I just put them on anyway and get on with it. I don't feel it's hampered anything. Pedaling a bike does seem to keep the fluids pumping well enough to avoid the fluid pooling in the feet/ankle area, but I know if I wear the compression socks it'll keep it that way.

Where I really notice the swelling is either after being seated for hours on end, or if I'm on my feet all day. If I stand up and walk around from time to time it's less of an issue. When I fly in an airliner I always wear them, because that's just DVT waiting to happen, and thanks but no thanks to that.

Anyhow, not everyone needs compression socks, but if you need them you need them, and I see no reason not to wear them. It's not like most folks with varicose veins or other circulation problems are competing in UCI-sanctioned events where they'd be banned. I'll be wearing mine more often than not.