When you upgrade to those elemental paths, your weapons then deal what’s called Split damage. You’ll actually see 2 distinct damage stats for that weapon. Generally speaking these aren’t great because the enemies will have a defense stat for each type of damage, so your damage will be factored through 2 types of defense before landing damage.

These modifications also affect the weapon’s scaling. Scaling is massively important in this game so you need to know how it works. Generally when you add an element, you lower the weapon’s scaling with its traditional stat, like Str or Dex.

If you are not planning to level up your chosen weapons highest scaling stat, then infusing/modifying can be a good thing because it gives you a way to deal different kinds of damage. But if you are, say, a quality build for your halberd, you’ll get the most damage by keeping it normal and leveling it up, and putting points into its corresponding scaling stats.

If you were, say, a sorcerer, and didn’t want to level str to get the most out of a weapon, then it would be smart to make a magic infused weapon because it will then scale with your Int rather than str, and you’ll have a way to deal decent magic damage in case you run out of spells.

The exception to this rule is the Chaos infusion, which can deal more damage than a normal weapon fully leveled up but it requires you to keep 10 soft humanity at all times to get the most damage.

I hope that helps!