I think what he means is to make the middle squares unmovable. If I hold the top and bottom middle squares and any of the side middle squares, I can still turn the cube. I think he means to make it unmovable that way. I could see how it would make it a little harder for some people, because then you would have to focus on a different perspective while solving it. Since I know the standard move solving, if I get to the last section where I have to solve for the corner squares on the last side, I typically rotate the entire front section. So if I could not do that (since the middle square is unrotatable), I would have to find other ways to move the end sections