Reduced operational cost

As we covered earlier in the book, serverless or FaaS applications run on the cloud provider in a fully managed environment. As there are only certain pre-defined runtimes where you can run your functions and the same runtimes are used by many other people within the cloud provider environment, the cloud provider is able to utilize the economy of scale effect and reduce the operational cost required to run your functions. The gains in cost that the cloud provider gets are also due to the fact that everyone shares the same infrastructure, including networking, and everyone will be using it only for a certain period of time rather than using it all the time, like in a traditional application. 

These reduced costs of running the functions are passed down to the people consuming these FaaS offerings. They are charged very little for the execution of the functions and are charged in ms intervals. You will see similar benefits in using IaaS and PaaS solutions; however, FaaS takes it to the next level.