There was a point (early 2007) where drawings were misbehaving by inheriting the scalelist from their xrefs. Excess scales could eventually degraded performance. Service packs were created (mid 2007) to prevent this behavior from continuing to happen. We could then do a manual "SCALELISTEDIT" "Reset" to fix individually affected files.
The new "Scale List Cleanup Utility" repairs files that were affected before the necessary service pack was installed.
So, if you find drawings that contain more than their original scales, you should use this new utility to correct them in mass.
Be Better... Eat your veggies!