When I first started making websites at the end of the 1990s, layout structures were table based. More often than not, all the sectioning up of screen real estate was done with percentages. For example, a left navigation column might be 20 percent whilst the main content area would be 80 percent. There weren't the vast differences in browser viewports we see today so these layouts worked and scaled well across the limited range of viewports. Nobody much cared that sentences looked a little different on one screen compared to another. However, as CSS-based designs took over, it enabled web-based designs to more closely mimic print. With that transition, for many (including myself), proportionally based layouts dwindled for many years in favor of their rigid, pixel-based counterparts.
Like all great designs and solutions, they come back around. The mini car, permed hair (I wish!), and flared jeans have all made their comebacks over the years. Now, it's time...