I've only done needle turn, and perhaps different concerns apply with fusible. I've heard people say that washed fabric will ravel more easily than unwashed, but I don't know if that's a concern when doing fusible. I wash everything, including my applique fabrics, and I've never had a problem. I learned from the Piece 'O Cake ladies, and they cut everything on the bias because the edges are then easier to turn (which, again, might not be an issue with fusible).