What are the benefits of having an overgrip on your racket?

Question

as oppose to just a regular grip

Answer 1

it doesn't fly out of your hand ;]

Answer 2

Overgrips absorb sweat better then the grip of a racquet allowing you to hold onto the handle better.  They also can be tacky to improve grip for some players.  The other benefit is you don't wear or tear into the grip of the racquet since these are hard to replace so when the overgrip is torn or worn down you can easily replace it with a new one.

Answer 3

Overgrips are used to increase the handle size. That's why it is better to get a racket with a handle too small rather than too large. And also it is easier to replace than regular grips, as grips tend to get very dirty or soaked from sweat.