I'm about to reveal my ignorance; can a Postal Money Order be cashed/deposited like a check in my bank? Or do I have to take it to a postal outlet to be cashed? The nearest such outlet to me does mostly passport applications and lines are out the door usually. Seems like it'd be a lot of hassle if other sales options are available.
Some people, for whatever reason, don't have bank accounts, hence the occasional use of postal orders. Rather more, perhaps, are suspicious of PayPal et al, hence cheques. Clunky, but I don't have a problem with them.
Occasionally I will sell small collections of surplus material at bourses to free up some cash for new material. I have a strong preference for converting this money into money orders vs. depositing in my checking. Would only use money orders with dealers I trust of course. So sometimes money orders do make some sense even if you have a checking account.