The idea looks good on paper but in practice it is pretty pricey and impractical. You get free sandboxing, scaling, and stateless deployment out of the box but are charged by the second. It's really optimized for simple web apps (or microservices) - think backend for form processing or resizing a picture. Anything moderately complex e.g. python scientific software is impossible due to the 50MB compressed app size limit (including all your dependencies), if your app takes more than a couple seconds of compute time, it will burn a hole in your pocket.
Usage: Algorithmic trading, Alexa voice apps, Brokerage price matching