tl;dr - What are the advantages of having handler and service methods separate housed in separate classes, rather than joined in a single class.
The premise seems to be that Triggers handle "when" the automation launches, a handler class handles "what" launches, and the service class handles "how" the automation works. I understand the basic ideas behind dividing functionality into distinct areas, but the separation of a handler and service class seems a bit excessive to me.
A practice I have been doing for a little while is simply having the "stoplight" considerations at the top of a handler class (aka, what fires when), and then below the stoplight code is a comment in the code stating the service methods are below, followed by the various service methods. The advantage I see in this model is that I don't have to have multiple files open, and can easily do text searches across my single file to locate code.
Since there is so much written about the service layer model, I imagine there is something I'm missing here, and was wondering if anyone could explain the clear advantages of having handler and service methods separate, rather than joined in a single class.