If you could play your game while editing a level for instance, it would cut down on development time significantly.
Imagine you are building a platformer. You run your game and you notice that you can't make the jump. To fix it you have to stop your game play with some variables and test it again.
To tweak these variables and levels to perfection takes time. This is multiplied by the load time of the game.
C3 is already built for speed, this would make the development process go by much quicker.