Actually it could be a maintainability nightmare either way. It depends on the structure of your site and what you are designing for. If your site consists of 500+ pages that is divided into 30 sections, all with different formatting, then external style sheets are nothing more than a headache. I have some pages that share the same formatting as others, but once you bring multimedia into the mix, a single page may no longer share the same formatting as other pages in its section. A “static” website where every page is the same should use external style sheets. Otherwise, who wants to edit 2 pages for every single one webpage? Some people cannot code all that fast, in this case they should use external style sheets. I can code a page out in seconds, practically with my eyes shut, I have no need for external anything. Also, alot of the time I just simply copy and paste a page to retain its formatting, then simply replace the content (this takes about 5 seconds of time), and the pages load fast because I’m not linking to a million style sheets.
There’s site popping up everywhere that have literally hundreds of external style sheets, goofy.