A few practical notes from Choice City Locksmith, a mobile locksmith in Fort Collins, Colorado.
Previous owners, contractors and neighbors may still have keys. Rekeying swaps the pins inside your existing locks so old keys stop working, usually for less than replacing the hardware.
Every copy adds a little error. A copy made from a copy can stick or fail, so bring the original key when you get duplicates cut.
Most cars from the last twenty years have a transponder chip in the key. A replacement has to be cut and programmed to the car before it will start the engine.
Use a dry lock lubricant rather than oil. It keeps cylinders turning smoothly and helps stop them freezing on cold Colorado mornings.