The extra space per character may not be much...but the total space across all characters IS. Even chars who don't even have Fisher unlocked need to have that space allocated to their character file on the server in reservation for if and when they DO unlock it. FFXI is a great example of what happens when the devs cave and give people a whole pile of inventory options. It now takes a solid 15s or so just to fully load up in a zone in that game. You load in and can move and interact but you can't access inventory for a good 15s or so. This is because the game is spending so much time trying to read and load up your inventory so you can readily access it. It would be worse in XIV since inventory is displayed dynamically as a UI element.