I'm not exactly 100% clear on it either. There is a dedicated thread and apparently people are stating they've arrived at Disney with room only reservations, haven't paid the balance in full, left from their trip, and then finally been charged and paid for the whole room (besides deposit) up to 7 days later? The reason being the system sometimes defaults back to old payment methods that are not valid so Disney is potentially losing out on money. I have never had this happen and always pay off my room only in full prior to arriving.
My main concern was also paying with gift cards. If the max charging cap is lifted because Disney will just keep authorizing $100, $100, $100, etc, I guess it could technically be easier and you would not have to pay off the room as frequently. I am a night owl and run to the desk every night when its slow and pay my balance off. I just like keeping track of every single purchase on the room folio and doing 1 big swipe.
I guess I will find out how it goes in March.