I know this is technically possible, but I've never seen it being used. This is definitely not the reason why so many sites disable pasting.
Coursera use it (plus a webcam shot) to try to verify that every coursework submission is from the same person.
Well they are trying to justify their certificates are legitimate, of course they use every cheater-catching trick they can. This is not just logging into a random site anymore, this is trying to do fraud detection for exams while not physically present.
(Also, one example doesn't make something true.)
> (Also, one example doesn't make something true.)