Users are part of previously defined groups with corresponding previously defined rights. Usually you do not need to create users, but use the item "Employees" in the category "Personnel" for this purpose. Users are needed e.g. for the call center or if you want to give an employee from the head office access to certain store-wide areas, e.g. the statistics for all stores. Accordingly, all users always have access to the data of all stores.
If you have a central accounting department that manages all your stores, this account can also be created here. In this case, however, the user would not have admin rights, but rather restricted access, which ensures that only accounting-relevant data is displayed.