Stamp prices and rebates
The Post Office raises stamp prices by tiny amounts frequently, instead of large amounts infrequently.
I bet they make a killing from people like me who won’t actually go through the trouble of buying 2-cent stamps to match my remaining stamps at the old price, so we either double-stamp everything or throw away the old ones.
It’s the government-sponsored equivalent of mail-in rebates: making money from the lazy or forgetful.