Keeping track of strait of grain is not so much of an issue if you are strip piecing the strips. Which is a pleasure to do, when one cuts nice straight strips in the first place.
I learned rotary cutting from a Judy Martin class, and I've used her techniques for a long time. I also ignore them, when it suits me. But I agree -- it's a good thing to know the "rules" and rationale behind them. Then, if you choose to do otherwise, it's an informed choice.
This however, has not been a popular mindset around here. <ahem> Watch out, or you will be called disturbing and forward.
RST