The term saving throw is common enough, coming to us from miniatures wargames and D&D. It represents the chance for the figure concerned to avoid (or at least partially avoid) the cruel results of fate. In AD&D it is the same. By means of luck, skill, magical protections, quirks of fate and the aid of supernatural powers, the character making his or her saving throw takes none or only part of the indicated results ...That's probably the most exhaustive explanation for what a saving throw is in the Gygaxian canon, but, coming as it does in 1979's Dungeon Masters Guide, it can hardly be called definitive for the entirety of D&D. (And if anyone knows of a lengthier or more detailed discussion of saving throws in Gygax's works, I'd be interested in knowing about it).
I bring this up at all, because my post last month on this topic generated a lot of valuable discussion, but also some disagreement. I treat saving throws, by and large, as a kind of check against a player's foolhardiness. It's a last chance to mitigate the consequences of his own stupidity. Quite rightly, some, including the estimable Dan Proctor, creator of Labyrinth Lord, disagreed with my approach, since it doesn't explain why a character should get a save vs. a spell cast by an opponent or why a fighter has a better saving throw against dragon breath than any other class.
That's a perfectly valid criticism and, in light of the text quoted above, illustrates that, like many things in D&D, there's no single overriding explanation for their existence. Saving throws have, so far as I can tell, a dual purpose. One purpose serves verisimilitude; saves are a way to represent the fact that not every attack is 100% effective all the time. The other serves "fairness;" it's a recognition that D&D is a game and people often better enjoy games when they feel "there's always a chance" that they might succeed (or at least avoid the worst effects of failure). Gygax himself was aware of this when he wrote later on in the same section of the DMG:
Yet because the player character is all-important, he or she must always -- or nearly always -- have a chance, no matter how small, a chance of somehow escaping what otherwise would be inevitable destruction. Many will not be able to do so, but the escapes of those who do are what the fabric of the game are created upon. These adventures become the twice-told tales and legends of the campaign.I rather like this passage and think it does a good job of showing not only why saving throws are themselves an invaluable game mechanic, but also why saving throws whose consequences are "inevitable destruction" lend richness and texture to a campaign -- which is why I do not now, nor have I ever, shied away from "save or die" effects.