Controversial question. How low are you supposed to go on bench press? Are you supposed to go down to the chest or a few inches off? Does this cause shoulder problems in the future? Or are you supposed to stop once your elbow and upper arm form a right angle? Everyone keeps telling me different things.
People very in the size of the chest and length of the arms. I’m a skinny guy, so when I bench (once in a blue moon), my arms go WAY past 90 degrees before the bar hits my chest. Some people stop much shorter because the size of the chest stops the bar. IANAPT (physical trainer) or anything, but I’d guess not going so far down as to cause physical pain in your shoulders. Also, good form should be practiced.
I take the bar all the way down. I try to take it down slowly and resist the urge to bounce it off my chest. My shoulder both pop a little during some movements. I also dislocated my right shoulder doing dumb bell presses 2 years ago.
If your shoulders are sore after benching, you’re probably lifting too heavy. You want to be able to lower the bar slowly to your chest. If it’s so heavy that you allow it to fall on the downstroke, then it’s too heavy. If you’re new to weight training, start off slow. You have years to injure yourself, there’s no sense being in a rush.
In a proper bench press (i.e., competition form), you start from lockout, lower the bar to your chest, pause, and raise the bar back to lockout. For most people, this is safe. Folks with poor shoulder flexibility or previous injuries may need to decrease the range of motion a bit. You should be more worried about not having your elbows out, which is a good way to hurt your shoulders.
I hired a trainer to teach me “how to work out without hurting myself.” When he showed me the bench press, he pointed out that, in good form, you don’t bring the bar straight down, as I thought. If it touches the chest, it’s below the pecs, not up by the collar bones. He said it works the right muscles that way.
Now, I don’t pretend to be an expert, far from it. If you’d like to disagree, maybe I’ll pass it on to my old trainer. I have no expertise of my own. If you call me a fool, it won’t be news to me. 
Going low shouldn’t be harmful to your shoulders but the fixed position your hands are in while doing barbell bench presses can be. Something a lot of guys who’ve been lifting for many years have in common is that we’ve replaced barbell bench presses with the dumbbell variety.
Agreed. The proper form for a bench press is actually a “J” motion. That is, the bar should touch the middle of the chest (about nipple level), but finish at eye level. The triceps are most in play at the bottom of the lift, when the bar is coming off the chest, but about midway through, the shoulders are more involved, and that interaction brings the bar towards the lifter’s head.
The reference to a 90 degree angle of the arms deals with how wide your grip is. Ideally, you arms form that 90 degree angle, meaning the hands are in line with the elbows (i.e. the hands aren’t too wide or too narrow). I once read that the easiest way to determine your natural width for the bench is to get into a pushup position; you’ll naturally position your hands at the right width (generally just wider then your shoulders).
I’m not sure why you wouldn’t bring the bar all the way to the chest on the lift. Doing so may allow you to lift more weight, but it’s because you are shortening your range of motion. Anytime you perform a lift, you are going to involve the most muscle if you safely perform the exercise through a complete range of motion. Doing half reps might be good way to finish a set when you’re thoroughly fatigued, but you’re robbing yourself of muscle development if you always “cheat” on the exercise just so you can tell people you lifted more weight.