According to the book High Performance Web Sites: Essential Knowledge for Front-End Engineers by Steve Sonders, and at BEST PRACTICES FOR SPEEDING UP YOUR WEB SITE, there is a best practice for boosting front-end performance as follows:
The problem caused by scripts is that they block parallel downloads. The HTTP/1.1 specification suggests that browsers download no more than two components in parallel per hostname. If you serve your images from multiple hostnames, you can get more than two downloads to occur in parallel. While a script is downloading, however, the browser won’t start any other downloads, even on different hostnames.
It’s easy to do this in WordPress, just add the following to your theme’s functions.php file
2. Forcing plugins to put JS at the bottom of the page
You’ll need to add a true value to the in_footer variable.
So, normally, in your plugin, you might currently embed a script as follows
wp_enqueue_script('plugin-folder', '/' . PLUGINDIR . '/path/to/your.js', $dependencies);
wp_enqueue_script('plugin-folder', '/' . PLUGINDIR . '/path/to/your.js', $dependencies, false, true);