I think when your party wants to fight very powerful enemies that all of them have magic weapons.
Who would attack a demon when you are only equipped with regular swords?

Just to be sure: DnD 5E makes only a difference between magic and non magic, right?
DnD 3E had resistences like 5/cold iron, 10/magic and so on.
In BG you need a macig weapon+1 for many enemies, some require+2, +3 is enough for almost everything and +4 was needed for the most powerful ones. (Kangaxx, Demigorgon, . . .)

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