You can use it on a multi city booking, through the call centre, and avoid the phone assistance/booking fees too.
For example I booked a BNE-MEL, MEL-x/DXB-LHR (switch between QF9 and QF1), LHR-x/DXB-x/MEL (switch between QF2 and QF10)-BNE. The multi city tool online would only offer me up to QF604 for the last MEL-BNE segment. All I had to do was ring them and say I want QF610 on the MEL-BNE (insert excuse) and I can't get that flight on the site to come up. They confirmed this was the case (you do need to be firm about it, ring back if you aren't having luck) and just booked it over the phone, sans fees.