All power levels are suitable for engraving applications.
More power equals more speed. As a guideline, a 50 watt laser will engrave at twice the speed of a 25 watt laser while achieving the same depth. Quality of engraving will be the same. In cutting applications, depth will depend heavily on the type of wood or wood product being used. For comparison, the list below contains the maximum recommended thickness of Pine and Walnut that can be cut in one pass with the specified laser power.