Piper used to wire panel lights with nav lights. A toggle on the old ones and a roller dimmer on the Indian series that would click the nav lights and then roll up the panel lights. Pretty sure Cessna always kept them on separate breakers. I should have picked a more critical example. Thing is, when wiring is new and done properly, all the failure scenarios are rare. As far as failures go, these simple circuits should never go bad unles the inevitable mistake shows up. Some time down the road something vibrates loose, gets pinched from unrelated maintenance, or corroded from improper placement, bad crimps, etc.
