Hi jdwertzier 
I use a number of sources along with my Guitar Tricks sub for instruction to ensure a balanced cross perspective and concensus from multiple viewpoints.
The perspective I've gleaned from all of that and [u]my own experience so far[/u] in [u]my[/u] answer to your question, is that there are general rules, but they are a base guideline as in "for the obedience of fools, and guidence of wise men".
Justin of JustinGuitar fame probably explained it best for me. Paraphrased, be flexible (figuratively speaking) so as to be capable of adapting to exercise the most naturally adept fingering assignment for the circumstance, which entails more than a single rigid assignment. Much like chord fingering really.
[br]An analogy to which I relate and you might be able to too, is the game of squash racquets where controlling centre court and minimising your own exertion whilst trying to maximise it for your opponent in your tactical play with inconsistent shots from lobs through drop shots, smashing drives or angular boasts is part of the strategic game. Squash is an exceptionally fast and dynamic "think on the run and adapt under pressure" game. I adopt the same approach to scales as pragmatically applied licks where my fingering is pragmatically flexible to be adaptable to use the most naturally feeling, fastest which achieves the sounding of the notes cleanly rather than one rigidly inscribed in stone of teaching convention even if I might respectfully start of with accepted wisdom of convention as my base starting point. Unlike mathematics, accepted convention in other things is frequently just because "that's how it has always been done" rather than being founded upon logic or subject to revisional review.
As a guideline, one finger per fret is the accepted wisdom, and while that can work just fine playing most scales as scales per se, in my journey so far I've discovered that not only are there specific instances where alternatives work better for me even in that regard, but IME the rigidity of that rule doesn't always work quite as well when applying them pragmatically as licks musically.
As I progress and my skills do to, I may find some obstacle in that to review and alter my perspective, but for now, that's how I see it and have chosen to apply scales in practice.
