We like to send them there so they can learn the defensive side of the game. It is quite common in the afl.
This wasn't a pot-shot about playing on the HBF - Vlastuin was actually a HBF in juniors so I have no issues with him playing there. He plays it well - though I do see him transitioning onto the ball in the future. I was just responding to a poster who accused the coaching staff of turning Vlastuin into a 'stock inside midfielder' - which is surely difficult to do when he's not even being played as an inside mid?