Wizo,
Not disagreeing with you, there are many scenarios re. PNR, particularly PNR to a moving base, ie: return to the carrier or another landing point, maybe a carrier or a land base, mil types will know all about some of the combinations and permutations that can cause serious brain fade. In practice, in my experience, PNR beyond destination means no more than somewhere you have passed, or the departure point, is covered as a conventional alternate to the destination.
PNR is not associated with distance, I don’t believe I said that, but in the “traditional” case, where PNR’s have a very very practical application, over very long range ( usually oceanic) operations where an alternate to destination cannot be carried, the calculation defines a place where a decision must be made to proceed, usually to destination or perhaps an en route alternate ahead, or return to an alternate, be it the point of departure, or some suitable alternate behind you, or off route.
Of course, in the off route case, an alternate somewhere abeam, there will be two points that will be equidistant from the off route alternate along your track, and one point where the distance will be minimum. Which is appropriate will depend on the day (or night) and the circumstances.
All this will be double dutch to pilots who only know about national or other rules that always require an alternate beyond the destination, or who operate aircraft over relatively short ranges, where it is all theoretical.
Over the years, I can recall some very long days and nights, doing seemingly never ending in flight calculations, working successive en route PNR3’s ( or PNR2’s really, now I had to re-plan assuming a further engine failure) to minimise the impact of % based variable reserves. These are about the only times I lamented the passing of the now endangered, if not extinct, pencil wielding homoerectusnavigatorous.
Tootle pip !!