Recessed Tonearm Armboards

A tonearm manufacturer once told me that a tonearm is restricted in movement if the armboard is recessed below the plinth. Now I have never owned a turntable that had a recessed armboard, but I have seen some that were recessed a few mm's to an inch, but nothing more than that. I wanted to know what is the reason that would cause the restriction or its ability to move less freely. Or maybe folks feel that it's just not the case.