Valid points.They are important, but not a must. I have run several FOWLR tanks that had no powerheads at all with no issues, through regular maintenance the tanks stayed clean. The main point I was making is running them during the cycle makes no difference at all unless you want to see where you have high and low flow.
What I'm trying to get at is that the powerheads make that maintenance a little easier especially in larger aquariums; it's not quite as bad in a smaller one.