Two of the major benefits of UA for non-frequent flyers are

1. Miles never expire as long as you have activity in your account (even non-flight activity) once every 18 months. All other non-US programs have expire date, which means old miles will expire no matter what depends on the FFP, every program has different expiry date of miles, some are as short as 3 years validity like NH and BR (there are many more but those two are the first I can come up), you have to read carefully

2. Award tickets have no fuel surcharge, for programs like NH or OZ, be prepared to pay a hefty fuel surcharge upward to $500 per ticket, compare with UA, the taxes and fees are likely to be less than $100, many times are less than $50 (depends on how many connections and where you connect)