Great ideal picture.
For those of us not achieving this in their day-jobs; fret not. It happens to all of us.
Not everyone has the resources to construct a full branding guideline, and having a general idea on paper, or even just a color scheme and some assets, is still better than having nothing at all.
Heck, if you're the sole designer, it's better to have an idea than no idea at all.
In other words; think about the principle in the article as an ideal picture, and see how close your resources can get you to it!
This is a great point. Also, different brands have different needs—it all depends.
Definition, context, use. A simple mantra for any guidelines.