The License to Kill

 What is the function of saving throws in old-school play?
What if their primary purpose was emotional rather than mechanical?
Why roll a saving throw at all? The general consensus around old-school best practices is that severe consequences should be telegraphed by the GM and therefore come as a result of the players' choices. A normal-looking door that shocks people to death is not allowed; but if the door has a sign saying "Keep Out! Wizard's Sanctum!" then it's considered reasonable. If the player tries to open the door, they made a bad choice and now they get the consequence. In terms of fictional consistency, there is no particular reason why there should be a saving throw. "Well, you've got to have some chance of survival." Yes, you already had that chance - it was called "not touching the trapped door"!
So the GM could just say: "You got shocked and now you're dead." But it's very likely this will feeling arbitrary and unfair to the player. The saving throw comes in as an emotional tool to give the GM some plausible deniability. It gives them a license to kill.
Both elements - the bad choice and the bad roll - need to exist for the death to feel fair.
(For death you can substitute any other severe and permanent consequence, of course.)
Perhaps other randomisers in old-school play also serve the same purpose. Look at encounter tables. All of the encounters on the table should offer agency to the players as a baseline. If one of your encounters is "5 red dragons, always attack from surprise" then it doesn't really matter if there's only a 1-in-100 chance of it happening, it's still bullshit. So to flip it around - if none of your encounters are bullshit, then why randomise them at all? Why not just pick whichever one seems appropriate in the moment?
The answer is: you roll so that when the players get into a fight, you have a license to kill.
The truth is it's all you (the GM). You wrote or chose the encounter. You introduced the possibility of death when you called for the saving throw. But the roll itself is a crucial point of emotional distance.
"Aw, sorry buddy. The dice killed you. Not me... the dice."