Your dive instructor career will likely provide you with some photo ops in beautiful places, and you might not have to pay for the trip to get there. You'll also get to see some babes in some hot bathing suits. Those are the obvious benefits.
The benefits aren't quite so obvious, but we'd rank them up there with the bathing suit bods. Let's say you get a student who's a bit lacking in confidence, but has better skills than she realizes. You work with her regularly, even coming in before class to give her extra pool time, and she makes slow but steady progress. Imagine your satisfaction when she passes her Open Water Diver certification exam with flying colors!
You might also have a kid, about 18, who seems more like a dolphin than a human. This kid knows more about diving and marine life than most adults twice his age, and he soaks up the Open Water Diver course information like a marine sponge. He could probably teach the class, to be honest, and of course he easily gets his C-card. When you meet him at a dive expo two years later, he's managing a Caribbean dive resort and making tons of cash. You really can say “you knew him when.”