What is the benefit of playing on 200cc?

200cc is there just for an extra challenge, though the tracks aren't designed around it (for example, you can go out of bounds in Dino Dino Jungle just by launching off a blue ramp).

It can also be used to help you get better combos by reducing the time it takes to travel through barren areas, though it's possible to boost your combo time (time allowed between actions in a combo) enough that you can chain miniturbos endlessly. This can be done by choosing gliders that favor the track in question and levelling them up by getting repeats of it.

I want to add to inakilbss answer that the experience you get from the race is higher, the more cc the race is.

So in the 200cc you would also earn more experience