There is a myriad of reasons that will wear locks down over time. The biggest reasons, of course, being environmental factors and erosion. Anything from rain, dust, and sand, can get stuck inside of a lock and begin to mess up the insides. Additionally, keys naturally lock-in and scrape and rub against the interiors of a lock, over time, the two will wear each other down into nothing.
Locks are repaired by making simple solders and repairs to these areas. It can be as simple as thoroughly cleaning the lock, to simply melting more metal or replacing parts of the locks, the procedure will often be much easier to manage if called in early on.
First off, lock repair isn’t for everyone. If you own a large apartment building and have over 100 keys given out, chances are it will be far less expensive for you to repair the lock instead of replacing all the keys that are there.
But if you are dealing with a lock that has important value, then it will only make sense to ensure that the lock is repaired instead of being replaced.
This is especially true for people who have high-quality locks or sentimental, ornate locks. Often family-owned homes for many generations will have locks and doors and parts of the home that are much more expensive because they are practically antiques.