Partials in WordPress, regardless of if they are part of a plugin or part of a theme, can help maintaining a project much easier (let alone building a project).
But if you’re working with them to help drive your settings pages or your WordPress administration pages, part of working with them is making sure they are adequately represented on the server-side, too.
Generally speaking, this is usually referred to as the domain logic or may even be thought of as part of the “model” or “controller” code when thinking regarding MVC. Of course, this isn’t MVC, and I’m no fan of trying to apply patterns where they don’t fit.
My point, though, is that I’m talking about object-oriented classes that are responsible for managing data and handling coordinating information rendered in the partials and how the user interacts with it.