I never cut fabric that I have on hand because it's too pretty so I just have to go out and buy what I need for a project. But seriously, I've gotten "cutter's remorse" when I do jump the gun and cut into large pieces. Sure as anything, as soon as those last threads are snipped and it falls onto the table in two pieces, the longest one will always be 1/2 inch too short. Have the pattern in hand and measure twice before you start whacking away. (Think of backings, one-block wonders, long vertical borders, etc.)