I've used them for four main reasons:

1) You're paying for something already going through the mail (e.g. sending a form to the government).

You can usually send a check, but some banks don't issue checkbooks anymore.

2) You're sending a payment to an individual online (e.g. eBay, Craigslist), and who won't accept online payments. Some merchants do accept PayPal, but raise the price to account for the merchant fee; a money order may be significantly cheaper for large purchases.

If it's a scam, it also becomes mail fraud and you have the Postal Inspection Service on your side.

3) You need to make a deposit payment to someone like a landlord. They often won't accept checks, because they can bounce. Money orders and cashiers checks are sometimes the only accepted payment. Of the two, a money order is usually cheaper than a cashier's check.

I need checks so rarely that I've never bothered to pay for any, and just use money orders when it comes up. I honestly think it's strange so many people in this thread have found them to be such a hassle, I just swing by the post office or grocery store and it takes two minutes.

This is how I used to buy stuff on Craigslist.

Also, if you ask the people you know and you might be surprised. Perhaps what’s more accurate is that you haven’t heard about it.

I vaguely recall having used one once, but I don't remember what it was for. Practically everything I've ever purchased has been via check, ACH, or debit/credit (with the largest purchases, like my home down payment, happening via cashier's check).

I've had a checking account my whole adult life (and then some), though. Some 22% of US households are either unbanked or underbanked (have a bank account but still have to use alternatives like check cashing services or payday loans in order to make ends meet)-- those are the people who are most likely to need to use money orders, even for routine payments like utility bills or rent.

I believe they're mostly used by people who can't afford to have a checking account but need to do something that would otherwise require a check. The poverty tax is real.

I use them whenever possible in place of checks. I have a hard enough time managing my finances without waiting for the money to come out of my account. Just my two cents!

I had to get one to pay a $10 or $20 parking ticket in Ely, MN in 2002. They sometimes come up in situations where paying cash for something presents a massive opportunity for abuse.

Imagine the cop who wrote that ticket being able to collect the fine in cash, and that's $10 into his or her pocket rather than $10 less overhead into the city coffers.

That's weird, every property I've ever rented from required that the security deposit be paid in a money order.

I used one to exercise stock options without spoiling the surprise by asking for wire transfer info

i use them to pay security deposits on apartments, since i still use a credit union that only exists in a city i haven't lived in for a decade

all banking i do online and their web/mobile presence is really good, so i don't really wanna switch, but there's no way for me to get cashier's checks, so postal money orders it is

postal money orders are really convenient for the limited purpose i need them for, and post offices are everywhere. i can imagine that they're much more useful for unbanked people, and think it would be really good to expand postal banking, but alas

Landlords were the last kind of business to accept online payments, and before that many of them preferred money orders.

I used them when I was in my late teens and did not have a checking account. I've used them since as well.