This rule actually can be used to generate all the other rules about spacing, kerning, leading, font size, padding, etc. It was the first true piece of "secret" design knowledge I was handed down when I went to work at an ad agency at 15, having already been proficient in Quark and PS/AI but without any formal design training. The rule about alignment based on eye / weight versus mathematical alignment also flows naturally from this.
Interestingly, it was the agency director who was not a true designer who told me this; I believe it was her one and only rule for judging design, and it worked quite well.
In the years I spent studying design and typography in art college later on, I never once heard anyone mention this rule. But it is the very first thing I bring up with designers I hire.
One thing that happens when you follow this rule is that you get an automatic grid of sorts, that isn't necessarily constrained to a standard way of breaking up grids. Using the same measurement increments (e.g. 10 pixels padding, or 1/2" gutters) as the multiple by which things that are lined up take their space from each other, you can get regularity and readability without boredom even in pretty wild designs.
Excellent job by this author putting these ... essentially rarely spoken, infrequently taught, but fundamental and quotidian design rules into a clear, digestible format. These are all things that are sort of assumed in design agencies but are rarely elaborated on so clearly.