Seems like too much work to prevent the juice bar from bursting and to actually enjoy watching the girls get fucked by the machine. Why not just let the players enjoy the scenes and choose when they want to inflate the girls.
That is why there is a "Fap Mode" where you can enjoy the growth compared to the main game. The main game is to unlock other characters, backgrounds, and so on. In order to unlock fap mode, you must complete each type of growth for one character. Keep in mind the unlocked fap modes are only for the characters you have done all of the growth types on. I hope this helps.