It is also possible to have communal locks (common entrance) on a master key system. This is where one lock can be opened by numerous differ keys, which is a popular setup with landlords who own a block of flats.
With this form of masterkey suite, tenants do not need to carry a key for the front door as well as their flat door key. The tenants can just carry their flar key which will also allow access through the main entrance door.
Landlords would hold the master key so that they can have access to the front door entrance and all the flats when required.
See the below example for a typical design layout for this style of suite.