It's fine to use the final round. It's ok if you are aware that it's your last round and you have a one shot bullet, then you use it. But only of the precious shots were used to try and kill enemies. If you just clip out, and unload all your bullets aiming at a wall, then you just aim for the body on a person, then you're a scumbag. I have a final round spear, but I never clip out. I always go for head shots. While sometimes, yes, I do get the one shot body shot, I still try to go for the head.