"Making arrangements" is never as good as being in a city that you already service, for you and for the airline. What if there was a minor mechanical issue? Happens all the time - you've been waiting for takeoff plenty of times with mechanics in the cockpit, having to sign off on paperwork. What if some other unforeseen delay causes the crew to go illegal and your quick stop in BOI turns into VX having to fly a crew in from somewhere? If any passengers need any sort of processing, there's no agent to help (and this can be as "simple" as someone vomiting on the ground and needing to disembark).