Saves as Severity

Saves in classic D&D come in 5 categories, and the exact categories evolved a bit from OD&D to AD&D, BXCMI, etc. Some thought has gone into tracking the different save categories, how they were meant to be distinguished, what they "mean", etc. Here's an observation I haven't seen expressed before: The save categories in OD&D are most easily interpreted as just levels-of-severity. Consider the following:

The first category is "Death Ray or Poison", and receives a +4 bonus in comparison to generic Spell saves for fighters (which we'll take as our baseline). Obviously, this is a category which represents instant death. In order to give our characters a fighting chance, a fairly hefty bonus is given.

Second is "All Wands -- Including Polymorph or Paralization". The emphasis on polymorph & paralyzation is interesting: these are effects that don't cause literal instant death, but do render the victim effectively helpless and subject to a follow-up coup de grace. Hence a relative +3 bonus is given to avoid these effects.

Third is "Stone", i.e., turn-to-stone (petrification). Similar to the preceding, a victim of stoning is immediately and permanently hors de combat. However, the victim is not quite so immediately subject to death, as the stony form doesn't allow an immediate dagger death-stroke. Presumably some amount of labor could break up the stone form, but that's a far more involved process. Bonus is +2 here compared to baseline.

Fourth is "Dragon Breath", which is not instant elimination from a failed save, but (obviously) pretty bad, major business. Bonus is effectively +1 in this case.

Fifth and finally you have "Staves & Spells" which is in some sense "everything else", i.e. non immediate death or incapacitation. This is our baseline, hardest to avoid, i.e., +0 bonus in similar terms.

Now, the counter-argument to all this is the position of "Wands" and "Staves" on the chart with the former (weaker) given an easier save, and the latter (stronger) given a more difficult save, which is counter to the observations above.

But more generally, you could use these principles for judgements on the fly about the severity of effect: basically you're awarding between +0 and +4 to the save, with more heinous effects given a more generous save (again, just to give the characters a fair, fighting chance). For example, I would consider giving the save for sleep (recall, "no-save" language doesn't yet exist in the OD&D LBBs) the same category as "paralization", since the effects are so similar. A bad falling-stone trap might be worth a save vs. dragon breath, whereas an instant pit-into-lava trap should be worth a save vs. death. Et. al.