These locks are very common because they are easy to understand and very secure. Their job is to always lock every time the door shuts. They are seen on exterior doors, restaurant wine caves, and other places where security is higher because valuable objects are contained within. There are usually automatic door closers installed on doors that have these locks so that people can’t forget to shut the door, meaning they are always locked.
Doors that have these can always be unlocked from the inside. A Schlage L series storeroom cassette retails for $233.