There are pro's and cons to Macca playing:
Pro's - Macca is a far more effective on-field coach than he is off-field, his mere presence on field makes such a difference to that side - and if you've ever had to put up with him in the coaches box on the sidelines, you'd know what I was talking about
Cons - his legs were stuggling to get through a game 2 years ago, and to deny a spot to an up-and coming who could fill the spot is a bit selfish - In my opinion only of course.
*edit* further to this, you would think that PNU have enough depth that there wouldn't be the need for coach to don the jumper.