? about benching at 90 Deg.

Since hight school i was told to touch chest when i bench and have always done so until acouple of months ago. A friend who is a pitcher with a shoulder sergery told me that bending the arms at 90 deg. is just as good as touching the chest, he said touching the chest works more of the ligimints then the chest itself, is this true, when i first heard this i was benching around 270(when hitting chest) now im around 350 ( doing it elbows at 90 deg.) am i cheating by not going down all the way, i also have problems with shoulders and find it much eaisier but i would rather do it right. and if the 90 deg. works just as well then why in comp. do they make u hit your chest? thanks alot for any replies.