The question of rekeying locks vs replacing them often comes up when a home is purchased. It’s a good practice to address the lock situation upon moving in cause you have no idea who may have keys. Spare keys can easily be made at various hardware stores, key kiosks, or the locksmith shops. With this idea, any number of keys could be out there. A good option upon moving is to eliminate this a possibility is to rekey or replace them.
Rekeying locks will almost always be the much more affordable option at accomplishing this. There are a few exceptions but for the average home, rekeying is generally always the best course of action. During the rekeying process the locksmith can also check for proper operation, alignment, and serviceability. Nothing worst than a lock that accidentally locks you out of the house while trying to bring in groceries.
The other side of this topic would be replacing the locks. Some folks just don’t like the look of the locks. Some don’t like knobs and would rather have a lever type lock. Some just like new things. Whatever the case is, if you do want to replace them, make sure to buy or ask for locks all from the same manufacturer to ensure keying compatibility. More often than not a homes I see one lock replaced with an incompatible lock. While there is absolutely nothing wrong with the lock, it just cannot have its key be shared by the rest of the locks.
One other thing to consider upon replacement is the original lock installs. Some locks from the late 60’s, early to mid 70’s were made with different length or to be specific, a backset. These can be challenging as replacement locks will not work in the preexisting hole on the door. One would just make the holes bigger. This isn’t the case. The holes have been drilled 1” away from the position that most current hardware suppliers make modern locks. In this case, a new door may be needed. A well trained locksmith will be able to cover these options for you if needed.