Why navbar and footer can not be built on a grid?

Question

css

I read the article www.cmsmagazine.ru/library/items/layout/design-cor... At the end of it, where the rules are listed, there is such an expression "- It is allowed to draw a header and a simple footer off the grid.". I also saw many layouts where the menu and footer were not on the grid. What are the reasons for this permission?

Answer 1

Nothing is true, everything is permitted (c)