I personally find them super annoying on mobile, where every little bit of screen space counts, even with a larger phone. Sometimes I'll accidentally tap them or they'll glitch or they take up a ridiculous amount of space. Ugh. If I'm gonna share, I know the button will either be at the top or bottom. I am indifferent on desktop.
I agree. No screen real estate will be sacrificed for these buttons. The content already has a max width, and the floating buttons will only appear when there's enough space beside the content. Otherwise they will appear below the content.
Easier to find, more likely for users to share (at least in theory).
Really? I'd form a blind spot on those things or hide them with an ad-block. I'd be more inclined to share something if it's good and could be of some help to someone rather than because I'm inclined to by the array of colorful squares on the screen. And how is "right after whatever it is that I'm enjoying" not easy to find?