How does a coating work?
Friction occurs between the material you are cutting and the blade. This friction automatically (and unavoidably) causes microscopic damage to the blade. In time, this damage mounts up to a point where the cutting edge becomes blunt.
Select a material whose characteristics slow down the damage process.
Select a coating which creates a thin protective layer between the cutting edge and the material being cut.
See the advantages of a coated blade over an uncoated one here...