Print Server User Assigned Printers is a feature of Simplify Printing to allow end users to select which print server printers they would like to use in their session. This is very useful in large environments where the users should be able to select their printers and having the administrator configure each user would be impossible. In the assignments pane, the administrator will see three places to assign a print server printer:

Admin Assigned: Printers assigned to this folder will appear for the user and cannot be removed by them. This folder should be used when the administrator does not want the user to be able to affect the building of these printers.
User Allowed: Printers assigned to the Allowed folder will give the user the option to build these printers. The user will see all printers under this folder when the user is adding a printer through the UAP application.
User Assigned: Printers assigned in the Assigned folder will be built for the user by default. The user can select to remove this printer from their session through the UAP application.
Now, with the UAP Application assigned to a user's startup folder, they will be able to select their printers from the list of printers you have allowed for them. For documentation on the UAP Application, see Print Server User Assigned Printers Application.