I mean obviously, in a "REAL" (all in capitals) Old-School game it wouldn't technically matter, because you roll 3d6 all in order with no switching around. But assuming we stop the fantasy-fucking-vietnam dick-waving for a second, or even if we don't, the question still stands.
Should, for example, someone who rolls 3d6-in-order and ends up rolling an 18 in Charisma have cause to rejoice, or should he bemoan his bad luck that it wasn't in Dexterity or Constitution?
I think, for my part, that people who run the type of game where the CHA 18 guy has reason to feel upset for the CHA 18 itself (not, say, because he really would have liked the 18 in INT so he could be a better wizard, but because he feels the 18 is "wasted" in CHA) are objectively doing it wrong.
Let's start from this perspective: those are the six ability scores. Charisma is in there. We must assume it is equally important (not necessarily equally in all situations but equally overall) to every other ability score.
If you're running the type of game where CHA doesn't matter enough for it to matter as an ability score (compared to the others), why the fuck are you keeping it?
In fact, as in life, CHA is generally the most important stat for getting ahead. More than INT, more than WIS, definitely more than STR. CON at least protects you from dying of an infection or something, so it gets an important plus there (you can't conquer the world with CHA if you're dead from massive infection).
But an old-school GM should be using CHA for all kinds of reaction-situations. Leading retainers/henchmen obviously, but it should be the stat the GM looks at in any social situation to see whether people take you seriously or not. Of course, other factors like social class can still matter a lot, but within your equal social strata, it is Charisma which will determine whether you do well: the pretty boy with the smile is more likely to get a second chance, or given the chance to talk first. It should affect how you deal with supernatural creatures, for that matter, and not just with the old canard of attracting succubi.
It should make you the party leader (again, things like social status aside) whether the rest of the party wants that or not; other people will see you as the most important person of the party (again, within the boundaries of the credible; if you're a 2nd level thief and the party has a 19th level world-famous wizard; he'll probably be seen as the most important person of the party, but then you'll be seen as the adorable youngster of the group and quickly develop a huge fan following).
It is a sign of the failure of thinking of some GMs (propelled, I suspect in some cases, by a common Nerd-belief in 'personality not being so important', and the utter fallacy that intelligence 'should be' more important than how good at making an impression you are) that people would think of CHA as a dump stat in old-school play. Of all the PC's ability scores, if he's only going to know one himself to keep in mind, that should be it. And it should be coming up as relevant in far more situations than almost anything else. Even in the common dungeon crawl it should be important, and if you get out of the dungeon and into anywhere there's people who can be talked to or social situations of any kind, it should be paramount.
And note one more thing: it doesn't need any kind of idiotic 'social combat' mechanics. It may not even need to be rolled; though I think stuff like retainer loyalty checks (modified by CHA) or reaction rolls (again, modified by CHA) can be helpful guidelines for the GM as to how people or creatures react to a player's roleplay. What Charisma should do is act as the lens through which the GM interprets the response to the Player's roleplay. A stupid idea or a really bad judgement of character (trying to bribe a guy who is unimpeachably honest, for example) should still fail, whether you have CHA 3 or CHA 18 (and no roll should ever save you from that, which is why new-school 'social combat mechanics' are bullshit); but the guy with CHA 3 should be beaten and sent to prison, while the guy with CHA 18 should be sternly upbraided and given a chance to explain his reasons for doing something so awful.
In my games, particularly Dark Albion: The Rose War, the players have quickly come to know the value of Charisma. And if you, oh theoretical OSR GM reading this diatribe, have been thinking of Cha as a dump stat until now, try to reconsider and understand just how great a gaming resource/element you're wasting by ignoring it.
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