Doing Dumbbell Presses Wrong?

ok - i was reading through some stuff in the max ot workout and there are a lot of suggestions as to form for exercises. one example - incline dumb presses - it says to rotate your palms inward on the way down and then again outward on the way up. It seems to me that would leave you with the dumbells in a position parallel to your body when u r in the lowered position. i have always kept them perpendicular all the way through the motion. Is there truly an advantage to the rotating? I have heard of rotating to have your palms facing you on the top of the motion to hit the tris, but never at the bottom.