Easy to upgrade. Creating a new server machine in Amazon’s cloud can be accomplished in a matter of minutes. So by using the service, you are always prepared to handle instant jumps in traffic. If a post jumps to the front page of Digg or Reddit, you can add more servers and balance the load. accordingly.
Cost-efficient power for large scale services. If your site attracts a lot of users, and eventually outgrows the limits of your regular hosting, Amazon Web Services gives you free hands in designing a server architecture that matches your needs, in a cost-efficient way, without needing to hire a complete network operations team to do the setup for you! This is how many of the most popular Facebook developers have built their servers.
Total control over the setup: Though this point might not be too important when running WordPress, if you want to get adventurous and build your next project using something more exotic than a combination of PHP and MySQL, you don’t have to ask your web hosting company. You install the software you wish, just like you would on a server of your own.