i have unwatched a few of the groups i joined or watched ... mainly those who i've asked to please remove me from their membership and they have failed to do so ... these are groups who post so many deviations that they fill my watch box and i miss seeing the deviations from people who i've friend'd ... i have unwatched only one deviant from those i chose to watch but this was because he wrote a journal that offended me beyond what i could simply overlook which is usually what i do when someone's feelings, beliefs, or thoughts are completely opposed to my own ... this deviant however went beyond what i could overlook ... it was unfortunate as i enjoyed his art, but his personality and mine clashed so much and after this offensive journal, sadly, i had to unwatch him.
Random reader interjection: You aren't dependant on groups to remove your membership. By using the "leave the group" option in each group, top left, you can quit and unwatch at the same time. You also don't have to watch group deviations. There is the option "manage friends", and you can choose whether you want to see a certain group's or deviant's works or not. I hope this was helpful
I only un-watch if the account was deactivated, even if there has not been update for 1 maybe 2 years I will wait and usually I like looking through a deviants journals and past works to see how serious or likable he is so I won't add rude people