It may allow you to work on variations to lines you are interested in studying.
Rematches

I never play rematches in live chess, I play 60 min games and normally don't have 4 hours spare. Online chess - yes if I enjoyed the game. OTB - of course, I get extremely expertised in the lines that we play.

I never play a rematch when I'm angry about a loss - because I know I'm going to play even worse and probably lose again :)
After a win if the opponent wants a rematch - sometimes. However there are players who get abusive if I don't grant them a rematch ... they think I don't want to risk losing after a "lucky" win or whatever ... but when I decline a rematch it's usually because I have no time - even at blitz, because sometimes I see I have a spare 15 min before having to leave for an appointment or whatever, that's enough for one 5 min game, but not a second one, so please think about that before getting angry about a declined rematch ...
Rematches are interesting because they tell you a lot about your opponent and even yourself. But they can be up and down sometimes. What I mean by that is that a lot of the time after winning a game your opponent will ask for an immediate rematch, and he's so caught up in getting vengance that he loses his patience and rushes moves only to make one bad move after the other. I'll be the first one to admit that I am sometimes guilty of this especially after coming off a loss to a weaker player. On the other hand some rematches can be great for your overall game. You and your opponent can be so evenly matched that you develop a healthy rivalry and these are the types games I love to play. The tension is high and the winner usually comes out on top due to just a minor slippage in his opponents gameplan.
Those are just a few of my opinions on rematches. What are yours?