The promo code limit I believe is the number of times the promo code itself can be used,
I believe we also need a limit for the number of times a user can use the promocode?
I think that both options are necessary. My last client was getting duplicated orders for the same thing because people didn't realize they had already completed the order. I think the best way to resolve this would be to put a limit to the promocode being allowed only once per user.