It gives a couple of classes that sometimes feel lackluster a bit of a leg up. Some will disagree that they need it, which is fair enough, but if you're using my aforementioned house rules on weapons, they open up the use of magic swords to non-fighters, which means you might want to give the grunts a bit of their edge back.
It puts an elegant Armor Class scheme for the "core four" into place, as pointed out by Brendan S:
- Magic-user, no armor, AC 9
- Thief, light armor, AC 7
- Cleric, medium armor, AC 5
- Fighter, heavy armor, AC 3
It avoids the "halfling hovertank" bug/feature that cropped up in the NYC Red Box B/X D&D campaign I played in (and, by extension, Labyrinth Lord). By the book in B/X, halflings can wear any armor and still receive their AC bonus versus larger opponents, which makes an agile halfling almost unhittable when engaged with typical dungeon denizens.
It makes fighters (and dwarves) look different from the other classes, which I think is nifty. If it's in plate armor and over four and a half feet tall, it's a fighter.
And if somebody complains that chain doesn't look as cool, do a Google image search for some Angus McBride artwork.