I always touch the bar to my chest, just been doing it that way for a long time however Im a powerlifter and its required to touch the bar to complete a lift. Many bodybuilders do not touch the bar to keep continuous tention on the muscles. Just depends on what your objective is.
I dont find this to be entirely true for me. My chest is not huge and I get constant tension when I touch. If it was the entire truth about the constant tension the pros would only be doing reps that are only a few inches cause their chests are so large, and besides to not touch would be kinda hard for them!
I think this is a very personal/comfortable choice. For me, I find that the lower down I go with the barbell, the more it works my front delts. So much so that it inhibits my bench workout. For this reason, if I'm doing a barbell bench, I'll go just a tiny bit past paralell with the elbows. I'd rather work the front delts individually than while I'm working chest. If I rely too much on the front delts to push the weight, the less my chest benefits.
For you guys, this mostly will depend on the size of your chest. If you're a beast, touching your chest may only be just past parallel.
I always touch my chest. I used to train with some guys and they always talked about how their shoulders were sore, they noticed that i never complained about my shoulders and yet always touched my chest. I think when it comes down to it, it may be the technique that may be causing shoulder soreness. Sometimes i have to check myself position while benching to make sure im in the right one.