I'm the only driver of my car, so that means I only use 1 key. Last month, the battery went dead in one of the remotes, so I dig out the spare key and remote. After owning this car for over 3 years, and only using the one key, I discovered the spare key was hard to insert into the ignition, and made the lock cylinder hard to turn, where the key I've been using the last 3 years was like butter. I decided to stick to using the spare key, as of now it's no longer hard to insert or turn. I learned that lock cylinders and keys wear together. From now on, every 6 months or so, I'm going to alternate keys, so they both work smoothly in the lock cylinder. I was worried about the spare key messing up the lock, or just not working at all. I realized it's important to rotate the ignition keys over time, so they all wear evenly with the lock cylinder.