I think on this subject we must remember that Jenny is doing a take-off of a traditional block using a precut. It would be much easier to start, in this case, with a square that is divisible evenly by 3 and add 1/2" for seam allowances. But because a layer cake is 10" those cut pieces and her final block are going to be oddly fractioned measurements, and sometimes biases where we normally would not put a bias, she is just showing her version....to fit into her precut fabric market. I think what she is trying to get across is - here's a quicker way to get a quilt done, using the precuts and a different way of cutting some of those shapes.......
I have read some cutting directions in mags that call for what I think of as odd fractions....like, ---3/8.....if I do one like that I will revamp the whole block if I can, or just pass on it...I hate those "off fractions". JMHO