Imagine you give your waiter a tip or gift someone else some sats via cashu as a present. If you see then after xyz time that they still have not redeedem your gift you can just take them back instead they getting lost/unused. Obviously as soons as they are accepted/reedem you can't get them back. So I guess what @Martti Malmi was saying is e.g. I could send you know now 100k sats in cashu via DM and say please build xyz into damus. And if you don't want or ignore my request I could always get my sats back without having to ask for a refund.