the boss sets have accessories from quests you do when you have the complete set. and the boss sets are very good for leveling, especially physical characters such as a buffalo. the element attributes (such as dark/wind/fire/etc) make it much easier to kill monsters/bosses.
in reply to "oh wow nonstop? wow....that motivates me to do the same!! i wanna do what she does!! can i do that with a buffalo? " in the boss drops thread: yes, you can do it with a buffalo. you can do it with really any character. just, it depends on which boss you want to fight and what eq you have/can get