I don’t know what started me thinking about this, but I did. Anyway, to answer my question:
- When it is neccesary. It is explicity stated in the AD&D PHB that a character that doesn’t have bonuses in at least two stats is unplayable and should be rerolled. Everything changed with that. Bonuses became necessary due to a sort of “false economy” that the rules established. It was like every design after that, whether it was monsters, rules additions, or adventures, was based on a “Holy shit! These characters are more powerful then they used to be! We have to ramp this <whatever> up!”
- When the bonus is the stat. I like this in systems where the bonus is what matters most. In every edition of D&D, since AD&D 1E, the stat proper has just been a scale to determine the “bonus”. Other than the cobbled-together mess of NWP, stats really do not matter. Some games have stats based solely on bonuses. Talislanta was the first I saw do that, back in the latter half of the ’80s. It isn’t really a popular paradigm, but at the same time it isn’t hard to find. The very cool Dungeonslayers comes to mind.
- When the stat itself is integral to the mechanics. In games like Errant the stat becomes a target number in a roll-under mechanic. I think it works quite well. I don’t have a problem with roll-unders. Some folks do, though. The problem with basing the mechanics on the stats is that it must be a roll-under to really work. Then, to make a roll-under work in a logical fashion, the stat has to be modified, not the roll. We are so used to modifying the roll that modifying the stat is a bit of a pause. The alternative is to reverse the application of bonuses, such that a negative number is a “bonus”. That is just too counter-intuitive to simply overcome. It takes work to wrap your mind around that.
On the whole I prefer either the roll-under or bonus-as-stat designs. They just make more sense. Also, remember, there were virtually no mechanics attached to stats in OD&D, at least officially in the LBBs. The supplement Greyhawk quickly rectified that, but as conceived, stats carried no intrinsic benefits. I suppose they existed as a means of comparison. I just know I definitely do not like the notion that a character is simply unplayable and/or undesirable with a shortage of bonuses. Especially when they are statistically difficult to come by. Couple that with the fact that the creatures and encounters are designed to challenge characters in possession of such bonuses, and it is an exercise in frustration to try to roleplay a character that is merely average.