Back in Ye Olden Days, you could stack multiple buffs of the same type within a group (i.e.: pally str + druid str + warrior shout). They "homogenized" them a while back where no matter what buffs you had, only the strongest one in that class applied to the group/raid. For example, your multiple group damage buffs would all "homogenize" and just use the highest-rated one.

It's worth noting that I wasn't joking.