[nurettin]

spring boot enforces the idea of having a service layer between controller and model to act as a glue between the two, so the controller can focus on controlly things like authentication and handling request s/responses (http,ws,rmq,whatever) and the service can handle creating objects, reading/saving entities and making calculations.

It just makes things easier to digest because you know what resides where. If I returned to rails, I would be using this approach more.