The ability to customize campaigns, set targets that are very difficult or nearly impossible in other programs (Targeting).
Bidding options can be limiting if you want custom bids from different networks/programmes like Google AdWords etc., but there's definitely room here! I've been using bid management software since day one when it was first released by my previous employer - this has now become our main tool so we don't need as much support staff at hand anymore which means more time spent managing accounts than actually doing them!!