If a custom field is being used in parent form (e.g. resource, project form) and a child form (e.g. booking, timesheet form). Then administrator can choose to use the prefill option, so the value from the parent form gets automatically filled in the child form.
Example: 'Status' field is common in Project form and Booking form. In administration >> Booking Form Layout, if administrator defines 'Prefill value from Project', then as soon as a project is selected in the booking form, the status of selected project will automatically get filled in the 'Status' field of booking form.
In this example, the project status gets filled in booking form, but it is not linked, which implies that if the project status changes after the booking is saved, then the new value from project form will not get updated in booking form.
If you want that status field in the project form gets linked to the status field in the booking form, then use the link option as show in the below video.
Tip: View video in 720 p quality and in full screen.
The same concept is applicable for fields which are common in project form and timesheet form, resource form and booking form, resource form and timesheet form.