The person Preference tab is used to identify assignment preferences for employees. The application does not enforce a user to set their Preference Profile.
Preference behavior is configured by your organization by authorized users in Setup > Preferences.
The information supplied is used to qualify, disqualify, or sort candidates based on assignment preferences. Preferences are either editable, allow reorder, view only, or a combination of user controls that are dependent on the selected preference. This means a user may experience greater control in one preference, and stricter controls in another preference.
For example, suppose the shift preference allows for reorder only, this means the user can only reorder the shifts available in the menu box. Suppose the area preference is editable, this means the user can edit the areas presented to the user. Multiple preferences may be defined, but if a date range is associated with a preference they cannot overlap.
Security permission settings in Setup control the ability to add or edit preferences in Setup > Preferences.
See Setting My Preferences topic.