Looking on from a distance, and not having seen the earlier unreferenced thread, I am quite surprised by the general tone of the replies. As I learned, one files a flightplan not in order to get any different treatment from controllers, but simply because it is mandatory. That is to say, it is mandatory for every flight that intends either passing through some part, however small, of controlled airspace, or crossing a national border.
Helen49's reply comes closest to what I learned, with one proviso: search actions will start when you fail to turn up at your destination a/d BUT ALSO IF YOUR FLIGHT PLAN ISN'T CLOSED. At controlled a/d's this is normally done by the controller, but if you land at a non-controlled field you must remember to call the relevant authority to close the flight plan.