Apple stuff seems to have the biggest difference in usefulness between new and used. The new stuff is usually really great, but as soon as they cross some "too old threshold" they quickly become next to useless because of how closed everything is and because Apple (and, shamefully, third party developers) don't keep up software support and backward compatibility. I've got a bunch of 8+ year old iDevices and Macs and they are all of varying degrees of uselessness as Apple and the whole ecosystem has abandoned them.