Think of it this way - if you had a piece of fabric that measured 21 inches long by WOF (let's say 42") and you want to get as many charm squares as possible out of that piece - I know that by using my ruler I can cut those 21 inches into four strips of five inches, and then I know I can get 8 squares per 42" strip. That will leave 1 inch strip of waste (total) after cutting all the long strips, and little 2-inch chunks left from sub-cutting the strips into blocks. And 32 charm squares.
It might just be me, but I am 100% certain I couldn't cut it that precisely in the Accuquilt. I have to leave some "overage" at the edges or I risk a block coming out too small, and with the piece of fabric I described there's just not enough "excess" left to get that many blocks. I might be able to get the 8 blocks across, but the 1 inch total 'fluff' room for all those strips isn't enough; I would probably only get the equivalent of three strips, so eight fewer charm squares.