For my range of motion (ROM), I bring the weight down until the back of my arm is parallel with the floor and this still hits the chest well and I get a massive pump. As you can see from the picture, this range of motion does produce good results for me and my chest, when flexed, does look okay. The reason I cannot go deeper than this on my dumbbell bench is due to shoulder impingement. Jason Huh, who is a professional bodybuilder, uses a limited ROM on his lifts as he believes this creates more stress on the muscle due to constant tension and I like to apply this theory to my dumbbell bench. Now for those who still are going to hate on me, letís see you do the same lift, POUND FOR POUND and with the same form.
For those who want to learn more about keeping constant tension on the muscle, you can see Jason Huh explain it in this video:
At the end of the day do what works for you.