This document discusses 4 key takeaways from 4 years of running serverless production systems. The takeaways are: 1) Serverless does not remove the need for strong engineering skills; 2) Serverless is "LessOps, not NoOps" - operations are still required; 3) Serverless is usually cheaper, even at scale; and 4) Serverless can be used for more than just a few use cases. The document also discusses Opsgenie's journey to serverless and examples of serverless applications.