Administrators have been "personalizing" lists and forms in ServiceNow for years. It's time to mix up the lingo a bit. Now administrator "configure" list and form views when they want to define the global default for all users.
In Fuji, "personalize" now relates to personal settings, as in specific to a user. User specific list layouts have been around for a while, but users could never control how forms look. With Fuji they can. By default the itil role has this ability, you can extend it to other roles. Once the admin defines the default form layout, privileged users can hide fields on the form but they cannot add fields.
Clicking the gear in the form header allows users to hide fields by either unchecking the fields in the list, or by clicking the remove icons displayed next to each field on the form.
For obvious reasons, users cannot hide any fields that could be set to mandatory in UI Policies.
What about client scripts that make fields mandatory? If the field is not mandatory when the form loads, the user can hide the field. However, if a client script sets the field to mandatory at some point using g_form.setMandatory() the field will reappear on the form.
Since the fields are only hidden, they still exist on the client. This allows admins to continue to leverage the fields in client scripts.
The last thing worth noting is that the personalization is based on a view. If a user hides a field on the routine view of a change request then views a record with the comprehensive view with the same field, the field will not be hidden.