The main thing in deciding to write a ruling into a rule is fairness. Because weapons are important in combat and are taken into the adventure, this makes it particularly important to establish their relevant characteristics as rules.
Fairness also applies to the referee. Once they've caught the impromptu ruling bug, players can be very proactive in pointing out situations where they feel they should get an advantage because of the weapon they're using. They may be more reluctant to point out their disadvantages, or the advantages of an opponent. Having clear rules about these situations makes it easier for the referee to put fair limitations on the players. You don't have to wait for the chance to turn the ad hoc rulings that enabled their own anti-monster tactics back against them.
So weapons are important - but how much should they be distinguished from each other? I'm very aware that simulationism can be a never-ending rabbit hole. Early D&D editions recommend themselves by their simplicity of combat resolution, their lightness of rules and stats. I don't want to throw that away. Hence my pledge to involve no extra dice rolls, and no looking up things beyond what can be easily written on a character card.
I've realized, though, that I do want to hold on to the article of faith that different size weapons do different damage. The argument that combat is so abstract that any weapon is an equal threat doesn't really hold water. If a dagger does as much average damage as a two-handed sword because it strikes more quickly, then the d20 combat system could have modeled that in pluses to hit, or (as in the roguelike game Angband and its variants) multiple attacks. I feel well supported in this by the expectations of generations of players and my own intuitive idea of what D&D is about.
Another judgment to take to a proposed rule: does it promote player skill and strategy, while not bogging combat down in minutiae of placement and timing? I think the kind of things I find important in weapons fit this bill. They are mostly about how the weapon interacts with a given situation, ensuring that players find it to their advantage to equip their fighting characters with more than just one weapon, and use these intelligently.
To end this post for now, I offer a set of ruling principles I use in my games, which in coming posts I'll expand into a set of weapon rules.
Disadvantages of Attack (hindering the free use of a weapon) give a -2 on a d20 chance to hit, and in opposed initiative, the disadvantaged person strikes after anyone else who is not at a disadvantage.
Great Disadvantages of Attack are also -2 to hit, but the attack happens only on the second round after engaging (at the normal initiative for that round), and every other round thereafter.
Advantages of Attack give +2 to hit and first strike. There aren't really any tactical situations that can give a Great Advantage of Attack as opposed to hindering the opponent in some way, though.
Advantages and Disadvantages of Defense in general combat are strictly applied to armor class, and are +/-2 for normal and +/-4 for Great dis/advantages - which way is which depends on how AC numbers run in your game.