If you're laying sod, the base needs to be loosened and worked up for the sod to take. A sod cutter will not do this, as a matter of fact, in many cases, it glazes the surface. The sod will never take before it dies. Round-up the existing, till it, rake the slag off, do your final leveling with a landscape rake, and lay your sod. Don't forget to roll and tuck your edges, and water the mercy out of it. Now, - if you wait long enough for all the foliage to dry up well, and till it well enough, many times you can get by without removing any or minimal amount of slag. If you're going to do this, you might as well do it right.