Another pro for o/w tickets is the ability to book multiple back-up tickets (e.g. book two return tickets a few days apart). This doesn't work too well if you're not Plat/1K/GS, as getting the miles back for the backup tickets would cost $100/$125/$150 (Gold/Silver/Non-Premier).
Originally Posted by
aacharya
Cons of OW:
1. Two change fees if both legs need to be changed.
2. No free stopovers or open jaws. (Well, by nature, two OWs can be open-
jaw).
If ticketing doesn't work online, then the are also additional booking fees for doing two one-way tickets.
You also lose the chance for a "free" one-way (
explained here).
Having a r/t ticket can sometimes help out when things go wrong... e.g. if there are long delays on the outbound part of short trip, it's probably easier to get a refund for a "trip in vain". (I've never actually tried this on a reward ticket).