Cshore there are some asthmatics that dont need a daily controller med like advair but those are only the really mild cases. Advair has to parts to it serevent which is basically a long acting albuterol and flovent which is a steroid to help with the inflimation, so if you were to stop taking the advair and just use albuterol as needed your lungs would become very inflamed rather quickly and you'd be using the albuterol a lot more.
and yes if an inhaler has 200 metered doses it means you get that many doses out of that inhaler