"I learned a long time ago how to hold a rifle tight to my shoulder...."

This comment brought to mind a question I've had for a long time. Why do the armed forces seem to teach holding the AR style rifles with the butt near the top, or on top of the shoulder?

I realize these are normally .223 (i.e. light recoiling) but how do they attain proper control of the rifle?

I would appreciate any explanation the campfire members can provide.

Jim