So I'm not 100% sure if this is an exploit, because I don't know if it's intended or not, but group buffs are not dependent on you staying in the group. So if you're having trouble finishing a quest because you can't quite do enough damage or something, hop in a warzone, get your group buffs and then leave. Assuming you had a varied group, you should now have an extra 5% crit chance, 5% damage, 5% healing, 5% endurance, etc... and it lasts for an hour.