How important is the cleaning of the combustion chamber in a pellet system?

Good day. How important is the cleaning (scraping off the soot layer from the walls) of a pellet system compared to an oil heating system? It is understandable that the ash container should be emptied regularly with a pellet system. But how often should the combustion chamber + grate not only be vacuumed out but also cleaned from soot on the walls using a metal scraper? Every year? After x? tons? Or only as needed, when a certain soot layer on the walls is noticeable? Thank you very much.