One excellent way to start a religious, superstition-laid argument is to ask how many keys should be on a automotive keyring - the idea was that if there was too much weight on it that the ignition switch could wear out.
Well, pretty much a whole bunch of things we once knew about cars is now outdated. The fastest way to stop a car with anti-lock brakes is not to carefully feather the brakes, but instead stomp on the pedal. High octane gas is not better for your car if it wasn't designed for it (though that said, the higher detergent that is often in expensive gas might help). And taking a lot of time to warm the non-carburated fuel injected engine doesn't usually make a whole lot of difference in how the car runs and is pretty much only good when the car is in the snow and you want some heat. So with that in mind, I figured that the whole idea that having too many keys on your keyring is going to wear out your ignition is likely hokum these days. Google searching is inconclusive. Even the lackies at Car Talk hedged and said well 10 keys is probably ok, but it you're a janitor you might consider separating the car keys out.
So with no solid information I cheerfully ignored the key adage and I would have continued to ignore it, until something completely unrelated to the health of one's ignition switch convinced me it was a good idea to separate them out.
At a shopping center near me there was a car jacking. Now that gave me considerable pause. Mostly because of the headlines if that happened to anyone with dogs in crates in the car. Most of these dog owners would rather be shot than let someone take their dogs, but once that scary scenario dissipated I was left with another one. If your keys are one one ring and you don't have a quick release, do you think that Criminal X is going to wait around while you take your car key off your ring? This is what unrealistic comedies are made of. So not only does your car get stolen, but they have your house and other keys and they have your registration which contains: your address.
Yikes. That more that any silly debate made me separate the car keys out from the other keys.