Is it true that if a reasonably big site (example.com) moves all its JS/CSS files and Calls them from an external domain altogether (like js.example1.com css.example1.com OR example2.com), the site will be comparatively much faster. If so why?
Browsers currently load only two items at the same time from one domain. If you put site furniture on another domainname, browsers start an extra two downloads for every different domainname. The maximum number of supported parallel transfers is eight in most browsers.
I don't know much about SEO problems, but I haven't heard of large negative effects.