To have the mod be able to tell the difference between, say, a flight on Kerbin, a flight into low orbit, and a flight to Duna. My reasoning is, I play with KCT and I need to raise the minimum crew r&r vacation time pretty high or by the time my next rocket is built, my crew is back from vacation, and it feels like the mod isn't even there, however, in my own personal playstyle I keep a separate flight crew for airplanes and space travel, and with the turnaround for airplane being hours or just a couple of days, before it's ready to re-launch, my pilots don't need a whole month or more to recover from a flight from KSC to the desert launch facility, but that's what I'd want for a trip to the Mun, Minmus, or Duna and beyond.