I have a couple of switches that to the casual person would appear not to do anything, but in fact they do. I recently added switch labels so I could tell them apart. Some possibilities like interior lights, trunk lights, or engine bay lights have already been mentioned. Perhaps it's a fuel pump cutoff switch for security. I have a switch to turn on/off a cool suit cooler for the track. When the cooler isn't installed it's just a plug in the trunk area. My engine builder has a low
oil pressure cutoff circuit for my engine. If the pressure goes below 20 the engine shuts off (mind you this is a dry sump setup). The engine will also not start until the pressure gets above 20. I have an override for this switch to start the engine after the
oil has already been heated. I also have an inertia switch override. I've had the inertia switch activate on the track by running over some serious rumble strips. I've had to be towed in twice (in 18 years) because the track workers don't reset the switches. My override will allow me to restart the engine and get to the pits to reset the inertia circuit without a tow. OK, that's all my switch secrets for now.