One way award flights can be useful if you only need to fly one way eg SYD/SIN and cruising back and a commercial airfare was more than half the return fare which they often are, particularly on full service airlines vs the LCC fares that are available on a way way basis.
For legacy carriers, although they may display the forward and return fare components separately, being able to pay the lowest fare is often on the proviso that you book and pay for the forward and return sectors at the same time.
Another instance where a one way award ticket may come in handy is if you travel quite a bit to a particular city eg SIN and you want to 'nest' fares to capitalise on the fact a SIN/SYD/SIN fare is cheaper than a SYD/SIN/SYD.
In that case you could do an award ticket SYD/SIN then purchase the round trip ticket ex SIN on the local (SIN) website of the airline concerned whereby the forward flight of that ticket gets you back to Aust and the 'return' flight SYD/SIN becomes your outbound leg of your next trip so you always have a SYD/SIN coupon in the bank.
This will only work if you know what date you'll be travelling SYD/SIN as the fees for any date changes may well negate any savings made from nesting the tickets.