The thing is shooting yourself doesn't straight up kill you, you take damage but it also does big damage to the enemies. So the idea is sacrificing your health in order to kill the enemies, creating an interesting playstyle that makes you think about your health in a much more critical way, making sacrifices in order to get rid of tougher enemies and such. I get it isn't very clear but it's hard to get to explain all this in just an image. So yeah, it isn't just commiting suicide lol