Comment by dec0dedab0de

I think its much more of a pain to have more than one language in the same file, but I suppose that's a matter of preference.

Some practical reasons for separate files, off the top of my head:

In-lining JS, and CSS means enabling unsafe-eval, which can open up XSS vulnerabilities if you use any content from users or gathered from a source you don't control. You could also do the unsafe-hashes, but that's kind of a pain.

If you're not making a SPA, it would not be fun to copy the CSS to all of your files.

If you do not couple your CSS to your site, you can reuse it across many sites and have the same style. Say if you have separate site for your blog, but want it to look the same as your main site.

If you're working on a team splitting things up into separate files will avoid some merge conflicts.

Chances are they will not be updated all at the same time, so caching would speed up page load times, as the user would only have to download the changed files