A few of the old-world dungeons in World of Warcraft that were truly epic places with more content then some of the later raids have been split up in the dungeon finder so it can be done a couple ways. Depending on the particular "mode", it changes who the final boss is, and knowing who it is is important for getting your bag of crap and other bonuses.
My problem is specifically with BRD, one way it ends at the warden ("Detention Block"), the other at the king ("Upper City"). Both start you at the beginning of the instance (unlike Maraudon where it will fling you half-way through it if you just need Princess)