It's kinda buried in all the announcements today but before this AWS Lambda could only be used for asynchronous calls. So if you were developing a mobile backend you could only process events asynchronously and had no way other than out of band push notifications to send data back to the client.
Now with Synchronous Invoke you can have a backend for a mobile app live fully on AWS Lambda. The benefit being you pay by the millisecond for compute time used vs having to keep EC2 nodes up and paying for underutilized instances.
