try dropping the bar onto the safeties when you're stuck in the hole and can't get out. Hell, in my rack if i am not perfectly aligned, the bar would probably fall and maybe break someones foot. With the position your body is in, if you're stuck in the hole and really can't get up, do you want to have to resort to maybe injuring yourself (getting a heavy weight off of your back when you're struggling to stay up is not easy) or having a spotter help guide you up. I can tell you this does help as i've had a spotter for squats before. I wasn't going to fail, but it definitely helps.