What happens when you get 100 percent in grand theft auto 4?

Answer 1

Nothing really, you can just continue playing the game as you were before the ending only without missions to worry about. If you have completed the game 100% however, your ammo cap will be broken allowing you to have unlimited ammunition.

Answer 2

Well if you get 100% in Grand heft Auto 4 you just get an achievement worth 100g and you get unlimited ammo