I don't want to be short cut or have wonky cuts because the folds aren't straight.
There is always a couple extra inches at my local shop. The owner and staff are generous cutters. Plus the owner frequently has a 30% off or finish the bolt (40%) off. Yes, I finish plenty of blots as I can't see leaving that small portion behind. I figure that extra is a little bit of insurance for my mis-cuts.
There are usually sales too when we attend classes or meetings. It's always a fun place!