Having the extra frequency/channel programmed in might be silent for now, but then it might become very active sometime later on.
I saw the old CNW PBX used once... basically the engineer just wanted to demonstrate how old he was...
Just returned from a trip on Amtrak, Minneapolis-Spokane-Minneapolis and I can tell you the BNSF people (both T&E and MofW) use their PBX a lot.