The Enchanted upgrade path is made available by ascension after giving Rickert of Vinheim the Enchanted Ember. It requires a +5 Magic weapon, Blue Titanite Chunks to upgrade to +4, and a Blue Titanite Slab to upgrade to +5.
Like the Magic upgrade path, the Enchanted Path increases scaling with the Intelligence stat and grants Magic Damage to the weapon, but lowering any Strength and Dexterity stat scaling bonuses and its physical damage. This makes it suitable for players with high Intelligence, but low Strength and Dexterity, especially when using weapons that have weak Strength or Dexterity scaling to begin with.
Enchanted weapons have even higher scaling with Intelligence than Magic weapons, but curbs Dexterity and Strength parameter bonuses more severely. However, with 40 or more Intelligence, Enchanted +5 will usually match or surpass Magic +10 in spite of the reduced physical scaling, making Enchanted the superior choice.
With the aforementioned in mind, the usefulness of Enchanted is most obvious for builds focused on having minimum Strength and Dexterity to invest as much focus as possible into projectile sorceries, as it gives an option to fight at melee range.