OD&D through BECMI uses a system of ability score adjustment where you can drop a score by 2 points to raise the Prime Requisite of your class by 1. I don't remember if AD&D does this as well.
It's something we did from time to time back in the day, but a lot of the time we just played what we rolled. Or we did a swap of the highest rolled score for the PR of the class the player hoped to play, with no adjustments beyond that.
I didn't include it as an option in TSR, partly because of the rules I'm using for rolling scores. Players can choose to roll 3d6 six times and arrange the scores as they like. Or they can roll 4d6-L down the line. I feel like allowing players to monkey with the scores on top of that ruins the whole point of forcing players to make this choice.
Anyway, one of my players was asking if he could do that the other day, and it got me thinking about the practice.
I'm wondering how often players took advantage of this back in the old days. Or how often players take advantage of it today. Since there aren't a lot of mechanical effects tied to scores, it would make sense to try and bump the PR up for a character. This gets a bonus to XP and bonuses to hit/damage for Strength, bonus languages for Intelligence, bonuses to saving throws for Wisdom, and bonuses to AC and ranged combat for Dexterity. And since the rules state a score can't be dropped below 9 (average), you can't give yourself a penalty in these areas.
I think it makes sense when rolling straight 3d6 down the line. You've probably got some scores that make you want to be a certain class, and then you can trade down scores your class doesn't benefit so much from to increase the one they do benefit from.
I'm guessing it was intended to be used by most players, to get "more viable" PCs, but I don't have any evidence, hard or anecdotal, to back that up. Just a gut feeling. If anyone has some insight or just wants to share how you & your group(s) do it, feel free to comment.
Anyway, time to reconsider how I do ability score rolls, and see if I want to bring this back in my games. Or not.