Before CSS Grid Layouts, creating a columnar styled web page was just a trial by error exercise in futility. Keeping track of your box positioning with regard to parent and siblings, using margins and padding to achieve just the exact result you were looking for. Then once it was all just the way you wanted it, the content itself changed and threw you back into the trial and error.
But with CSS Grid Layout, you develop the content seperately from the presentation of the page. Allowing you to change the content without really altering the presentation or vice versa.