upvoting, will put you on some trending hot list if you are powerful enough, hence increase your visibility.
I tend to do that for some reply I do, when it is overcrowded with answer and I think what I say matters.
Also there the curation reward link to upvoting.
Last point, it is the default setting when doing a post (so people aren't necessarily obnoxious , they just don't pay attention to it... )
agree