I use it all the time. Very convenient for keeping track of threads you don't feel like reading immediately.
This thread, Guess Who Is Next! and Server Problems, Post Here! are mine. Now one might wonder why we would 'watch' a thread that we aren't actually watching.
I'd say, generally because they're automatically "watched" when you post in them, while that doesn't mean that you're interested in always immediately reading new posts. I do it often for for example giveaway threads, I keep them in there for some time before I read them again, as constantly getting alerts for one or two people asking for a number isn't that useful, in my opinion.
