The way I see it, you want A-players in certain positions where their performance and influence drives the company forward - "moves the needle", to use a clichė. You don't want A-players in mundane/support roles because they'll end up getting frustrated and likely become disruptive (the exception is when you put an A-player in a support role so she can learn the ropes/basics before you move them to the role you actually want them to fulfil).