Good question! I currently use two for my own crafting and glamours and one for FC needs (with some overlap). I picked up my third during the start of the expansion since I'm second in command for our FC at this point. Which means I have one retainer which is basically a mix of food, airship rewards, and live auction goods. I host a bi-monthly live auction in our FC basement where we do live bidding for various things with a /random discount for the winner. Its super fun but does indeed take up some bankspace.