There are several reasons why the grouping of selectors benefits a page. First off, your stylesheet is smaller and loads more quickly. Admittedly, style sheets are not one of the main culprits when it comes to slow loading sites. CSS files are text files, so even really long CSS sheets are tiny, file-size wise when compared to unoptimized images. Still, every little bit counts, and if you can shave some size off your CSS and load the pages that much faster, that is always a good thing.