The #1 way to speed up your website is to minimize HTTP requests, however; inevitably you will make request for images, audio, video, code, and other content. Whenever; you can off load some of the content to other domains or to other servers your site will always load faster. However; there will be times when those ‘other servers’ will be down. Whether it is just for a moment or for a longer period of time, you do not want your site to be at the mercy of those servers. What can you do? (Glad you asked). You can have the best of both worlds. Why not check to see if the ‘other’ server is available. If it is then use their servers to deliver your content. If not then just load your own content from your site. It is not that hard to do and takes about 3 more lines of code. You can use this for anything in particular. Just find the piece of code to check for.
I am giving you this example of the jQuery library and any library will do just replace the code with the syntax for their library. Learn More