The process of changing the internal components so that a lock can work with a new key is Rekeying. Many reasons for rekeying the ignition depends on the following factors: -
Customer wish: When a customer finds that it is easy to rekeying rather than changing the ignition cylinder altogether.
Need not to carry two Keys: An auto locksmith can rekey the ignition so that the customer need not carry two keys for operating the vehicle. When a car owner replaced the ignition, he did not get the same key as the broken key. The old key still used to work on door and trunks. As the new and old key often look identical so it creates confusion. It is better to rekey the ignition as the process is quicker and cheaper.
These are the services done by an car locksmith. From Getting keys out from the trunk of the car to duplicate the keys, replacing ignition switch there are many things done by an auto locksmith.