This is a very simple and super light weight (1 line of code) add-on that simply turns off the extra loot frames that show who won loot and covers up your screen right after you kill a dungeon or raid boss.
The code is only one line:
BossBanner:UnregisterAllEvents()
I did not come up with this idea. It was written by Gello on Hyjal. I am simply turning it into an addon for you. He deserves the credit.
You can find the original post here:
http://us.battle.net/forums/en/wow/topic/20042934931
To turn the frame back on, simply remove or disable the addon.