It's my cousin's birthday. I can't think of a suitable gift. I go to the bank and get a draft (cashier's) check for $100 payable to my cousin. (It's an example scenario. No need to compare it with personal checks or with gift certificates.)
On the birthday, I give the check as a gift. My cousin puts it in a folder "to be processed on the next trip to the bank" but forgets about it. The check is never cashed.
What happens to the money? The bank doesn't even know how to contact my cousin (they just have a name). Suppose I'm still a customer of the same bank many years later. Will they contact me eventually and say "your $100 were never cashed, please come pick them up"? Will they wait 75 years and give the money to the state, as with dormant accounts whose owners vanish? Is the money a profit for the bank, until/unless cashed?