The space of one of my retainers is taken up by all my crafting mats (have all the tradeskills) and materia I haven't attached. My other retainer has all the items I've made waiting for them to sell on the auction
Instead of throwing stuff away that I'd use later more inventory space would be great, don't see why this game doesn't use a bag system and some developer said 7 slots should be enough when it's not