Yeah, especially when I started running 25man speedruns of Ulduar, it was quite nice to be able to skip all the optional bosses, and tell everyone "we're going to get these done AFTER we clear the raid, so if people want to stay for those after, cool. if not, they can leave and call it a day."
Especially on progression, it makes SUCH a big difference to bypass some farm bosses to get to the meat of the raid early, while everyone's still fresh and attentive.