If i kill a boss in a regular raid can I go back and kill it again? I get a toon saved to one boss and its hard to find a pug that has only the 3rd boss down. I was hoping that I can go back in there and clear the whole raid but I just wouldn't get any loot from the boss I killed already. kinda like LFR does. Thanks for any help.
No, you cannot come back and kill it again. You won't even be able to join a PuG that has that boss still up. Only LFR allows you to kill bosses as many times as you want (but you can't loot).
The problem is that when progression ranking is a concern, you could theoretically just hire a bunch of players who've already killed the boss to make it easier for your guild to progress.
Also, loot isn't individual, so it makes loot-stacking too easy for motivated groups.