No play = no travel?

Can someone clarify this? And explain it?

I thought I heard Jim/Hokie say yesterday during the game that Joe Horn was not at the game, that Payton's rule was if you weren't playing, you don't get to travel.

Is that right? Any reason why? I would think you would still want him on the sidelines helping out and supporting his teammates. It's not like he's suspended or anything negative.