This isn't an original idea of mine, I'm sure I read it on someone else's blog years ago. I have no idea whose blog I read it on, so I can't give credit, but I'll at least admit up front it's not something original.
I've been reading Jesse Schell's The Art of Game Design: A Book of Lenses. Over the weekend I read the chapter on game balance. It got me thinking of several things, but this was one that especially stuck in my head.
In OD&D, the only real reward for high ability scores was a bonus to XP, that represented the aptness of a high ability score towards the chosen class. Then supplements and later editions started adding other bonuses for high ability scores. Yet, even though there were now other bonuses of high ability scores, the XP bonuses have remained, at least through 1E and BECMI. I don't have the books handy to check if they were still in 2E and don't remember off hand. They were definitely absent from 3E forward.
Strength gives bonuses to hit and damage in melee, and to feats of strength like opening doors, bend bars/lift gates. The specifics and numbers vary, but Fighters get a bonus to their main function in added effectiveness, AND faster progression.
Intelligence gives bonus languages, and in some editions additional spell power (more spells learnable, greater chance to learn a spell, etc.). And for Magic-Users, also faster progression.
Wisdom gives a bonus to saves vs spells, and in certain editions bonus spells to Clerics. And Clerics also then benefit from faster progression.
Dexterity gives bonuses to ranged combat, AC, sometimes initiative, and in some editions bonuses to Thief skills. And Thieves of course get the bonus to progression.
But then, if we're playing in an edition that rewards high ability scores in this way, especially in editions like AD&D 1E that give more benefits for high scores, playing a character with average ability scores is a double whammy. You're less effective at your class's niche, and you progress more slowly.
What if that was changed? What if the 10% bonus to XP was for playing a character with AVERAGE prime requisite?
This small change would shake up a lot. It would add a new type of choice to character creation, especially when rolling for ability scores down the line. If you really want to play a certain class but don't roll high stats in that Prime Requisite, instead of point shifting, you would have some incentive to still play that class.
By the way, I did consider the effects of giving a 5% bonus for an average PR, and 10% bonus for a below average score, but I think that would be taking it a bit too far. I still think character classes should play to type somewhat. A weak fighter or a dumb MU should not be seen as a good choice. But a choice between an average Strength high Intelligence Fighter who isn't quite as optimal in combat but levels a little faster or a typical Magic User with plenty of languages and spells in the spellbook but with standard progression is much more interesting.
I haven't decided to try and implement this into my games yet. Since I run Classic D&D, there aren't as many bonuses for high scores, so this might only be a balancing option for Fighters (and demi human classes), with it giving too much advantage to the other classes to play a character with an average score over a high one. But it's an interesting idea to toy around with.