well if i do one arm Press i can use more weight and can CONCENTRATE on one side(great if you have a weak side) have even seen one arm Dumbbell bench press too. you can do more reps for a weak side too...However unless you hold onto a stationary object with one arm presses you cheat a bit more(i find) so both arms at once in my opinion are stricter although less weight... more weight is not everything.. i go more for strictness myself. the answer would be to also try alternate Dumbbell presses...
