There's no such thing! There's a half and a five-eight, and that's all there is!
Sure but suppose we are planning to shift the ball from the right post. That's a big blind side, and a fairly common position to attack from. The 'halfback' is keeping the middle defenders (including markers) honest at first receiver on the right, with his edge forward, centre and winger outside him, plus a tight forward off his inside shoulder. Meanwhile the 'five-eighth' is out on the left with his wing, centre, edge forward and the fullback outside him. You want to get the ball out to the 'five-eighth' but the dummy half doesn't dare try to throw a long floating pass that far because the 'five-eighth' will get smashed, if the pass isn't intercepted. You also can't just put it through the hands because the defence will read the play too easily and also smash the 'five-eighth' as he receives the pass.
The solution, used by both Des Hasler and Brad Arthur (among other coaches to varying degrees) is to employ a first receiver that doesn't just catch-pass, but provides a ball playing threat to a 'decoy' runner (who has to be a genuine option in order to effectively function as a decoy) and therefore keeps the defence honest, allowing the deep pass to the 'five-eighth'.
Not many players can effectively make this decision (whether to pass short or out the back depending on the defence), nor are they able to make both the passes required for the defence to feel properly threatened. You could use the 'halfback' whose side of the field is 'blind' for that play (and plenty of teams do, including Manly), but if he is looping from the blind to the open then you're removing the blind side as an option (unless you have a playmaking edge forward like Glenn Stewart) and telegraphing which way the play is going. That helps the defence make the right decision sooner, which the attacking team certainly doesn't want to do.
