Guild A is a 200+ member guild that frequently kills off MC.
Guild B is a small guild, @90 players, but can only field @20 people per raid.
Guild A offers Guild B a chance to kill the first 2 bosses in MC - Guild A will fill the raid out and add /recruit 15 other people and supply 5 "knowledgable" escorts to get it done.
After the 2 bosses are done {Luci/Madg} group leadership is passed to one of the 5 Guild A members - and 35 people disband. At this point the group raid is reformed with 35 new Guild A members to continue offering more chances at the last bosses/loot for Guild A member.
Cascaded instances do not save you to them because they are expired yet they still have loot tables.