Sam Newman and Martin Fowler discuss the reasons for using or not using microservices and the changes required for maximum benefits. They explore the benefits and costs of adopting a microservice architecture and the importance of clear goals and outcomes. They also highlight the top three reasons for using microservices, including independent deployability, isolation of data and processing, and enabling organizational autonomy. The concept of independent deployability is further discussed, along with successful deployment models in monolithic applications and the advantages of microservices in reducing the scope of deployment.