So there are 2 ways the game blocks you from going out of bounds. I refer to them as soft block and hard block. A soft block is anywhere where you can go but the game takes over your tank and takes it back into the level. A hard block is an invisible wall that only you enemies can go thru. You can however get through a few soft blocks if you have enough momentum and the area where the soft block is is small. I found 2 levels you can do this trick on, levels 1 and 9, but both of their final objectives are invincible. So as far as I know the only good out of bounds tricks would be on levels with boss triggers or mission triggers. Levels 2(maybe), 6, 10, and 15 could all benefit from this. I have yet to find a way past hard blocks though. It would probably rely on some sort of clipping similar to level 16.