DFC, Vintage ATCO is correct. 99% of airfields will either not receive or take any action for an en-route flight plan. So many pilots change there routing, i.e route around CAS without talking to the ATSU most airfields would have to have someone on the phone all the time taking overdue action.
However, you destination should alway action your FPL. When you depart they should receive a departure message from your origin if your flight is outside CAS. Your ETA is then calculated from this and overdue action is taken from this time.