For example, let's say @Slavik creates a new thread with a competition for guessing how long XF ticket reply times are. I put in my own (insanely funny) answer and now I'm watching the thread. I enjoy reading other people's funny answers (especially @Azhria Lilu , @whynot , and @Mike Edge ), but not every answer makes me necessarily want to respond. Instead, I'd just like a steady stream of funny answers into my inbox and I can choose when to jump in. But, to do this, I have to keep visiting the thread so that I will be updated with new funny answers — even when there's an answer that is not funny and that does not make me want to visit the thread! That doesn't make any sense...
Now, I'm not saying this should be on by default, but I'd like the option.
(Another example: I'm watching all threads on our forum. Someone asks a question that I don't know the answer to. I'd like to know when my colleague answers both so that I know I don't have to remind him and so that I know the answer now. I don't want to have to click on the thread every time my colleague asks the user for more information.)