The most common first move after losing a garage door remote is to just buy a replacement and program it in. The old remote still works perfectly fine, so it feels like a quick fix: grab a new one off the shelf, clip it to the visor, done. The problem is that the lost remote still has full access to your garage. If it fell out of a car in a parking lot or was taken along with a stolen vehicle, whoever has it can open your door any time they want, even after you've added a new one. Programming a replacement without clearing the old codes solves the inconvenience but not the security risk.