How much damage it adds
Each Sharpness level adds roughly 0.5 to 1.25 bonus damage depending on the weapon and version; Sharpness V on a netherite sword substantially raises the hit count needed for common mobs. It applies to swords, axes and (in newer versions) the mace's base attack.
Sharpness vs Smite vs Bane of Arthropods
The three are mutually exclusive. Smite adds a large bonus specifically against undead (zombies, skeletons, wither) and Bane of Arthropods against spiders and other arthropods; each is stronger than Sharpness for its target but useless elsewhere. Sharpness is the generalist — carry it unless you are farming one specific mob type.
- Sharpness — all mobs, the default
- Smite — undead only, very strong there
- Bane of Arthropods — spiders, silverfish, endermites
The standard sword
The usual 'god sword' is Sharpness V, Looting III, Sweeping Edge III (Java), Unbreaking III and Mending. Sharpness and Looting do not conflict, so the mob-farming and damage roles combine on one blade.