So, [MENTION=48965]Imaro[/MENTION], in your opinion, what's the point of having the three damage types? I mean, that was a 3e addition to the rules. Apparently we managed to play D&D for twenty years without it. So, what did adding those three damage types add to the game and what impact did they have on combat mechanics?
The damage types existed in 1e and 2e.
I don't have access to my 1e PHB so I can't say one way or the other if it specifically makes any mention of damage types. I wouldn't be surprised if the weapon vs. armor table was taking damage type vs armor via the bonus and penalties to hit.
However, different damage types mentioned with different effects do appear in the Monster Manual skeleton entry:
Skeletons "suffer only one-half damage from sharp and/or edged weapons (such as spears, dagers,swords). Blunt weapons such as clubs, maces, flails, etc. score normal damage)".
For 2e: Weapons are listed with a Damage Type (or multiple types) in the PHB" B=Blunt, P=Piercing, and/or S=Slashing. The damage type could alter a weapon's effectiveness against different armor types if using the optional weapon type vs. optional type.
Despite the optional effectiveness vs. armor, the damage type again has varied effectiveness against some monsters. From the 2e Skeleton entry:
"The fact that they are mostly empty means that edged or piercing weapons (like swords, daggers, and spears) inflict only half damage when employed against skeletons. Blunt weapons, with larger heads designed to break and crush bones, cause normal damage against skeletons."
So even if people ignored the weapon vs. armor table in 1e and the optional weapon type vs armor rule from 2e, certain monsters were affected differently by different weapon damage types in the 20 years before 3e.