If you're boosted you can worry about gear once, you can do diferent Flashpoints, you can do PvP diferently, you got more skills to use... theres loads of things you actualy get when you boost that can make the game more fun even when doing lower story quests. Not to mention way faster battles while blazing through the story and the worlds you need to clear...
This is the first MMO I see that offers the boost system and actualy completes the quests, it realy makes no sense to me like this.