Possible duplicate of:
should-i-link-to-google-apis-cloud-for-js-libraries
also many other discussions, including:
Where do you incl
I believe that the Google JSAPI is also asynchronous and helps avoid the "toll booth" best described by "Imagine there's a 4-lane highway between your web browser and the internet itself. This highway is optimize to let pictures, text, and css fly by. But, when it comes to external scripts, the highway creates a toll booth that slows traffic. The worst part is that pictures text, and css caught behind these scripts have to wait until they pass through" - Andres Vidal
The toll-booth is critical and must be avoided at all times.