Reentry mean, you finished the tournament, and if you buy in again, you start all over at a new random table. So for this kind of tournament I would basically just look in the lobby and see, what is available, that I might want to play.
If I got coolered in the first 1-2 blind levels, then there was probably a reason, I choose this tournament, and that reason is still valid. However if I have already been playing for an hour, maybe a new tournament has already started, or will soon begin, which I would now prefer.
Currently I play at
888 Poker, where there is no reentry but instead rebuy. This add another important element, where my decision will depend a lot on, weather or not I like my current table. If there are some huge fish, I usually rebuy and hope to not be moved to another table anytime soon. If on the other hand there are only solid regulars, then I typically just register for another tournament instead.
Other reasons to not rebuy include, if I want to close down the session, if I am tilted from the way, I busted, or if a more attractive tournaments is starting soon. In general I try to not rebuy to much, which also work as a form of
bankroll management. Rebuy on every single opportunity can lead to racking up some really big losses in a session.