Accurately notating any slab defects is fine, such as chips, scratches, etc., regardless of how severe, or not severe, such defects are. I think the issue might be that MCS' reputation for harsh grading has extended to the grading of the slabs as well, where slabs with barely perceptible defects are listed as "scuffing to front and back of case". I just assume this will be listed on every slab I send in and now just ignore the notation altogether, as buyer and seller.
To me, if the standard is so low that a huge percentage of slabs are listed as having scuffs as a matter of policy then the notation has stopped serving its purpose.