It can be interesting to remove access to certain screens from all users or to defined roles (e.g. restrict access to "budget" screen which may contains confidential information).
You need to be « Administrator » of the environment to define who is able to access the different screens.
Screens' access is defined by profil.
You can define screen access from the menu "Project".
Click on the name of the environment.
Then select "Screens" in the popup
You can then specify who will be able to see which screens
Be aware that "Administrator" and "Portfolio Manager" roles' access can be added to other roles' access. For instance,you can view the "buget" screen as "Administrator" and can't see it as a "viewer" of a projet, that means you will be able to see it anyway because you are administrator of the environment.