The MVC folder structure is easy to copy. The harder task is keeping each layer responsible for the right kind of knowledge.
Controllers are HTTP coordinators
A controller should know about routes, verbs, model binding, ModelState, authorisation, and response types. It may coordinate a workflow, but it should not become the only place where the business rule exists.
The first sign of a controller taking on too much is often a long action that loads several unrelated records, sends email, modifies roles, and constructs HTML. That code may work, but it is hard to reuse and difficult to test.
Services are reusable decisions
A service is valuable when a decision or integration is used by more than one endpoint, needs its own tests, or would obscure the controller’s HTTP flow. Examples include employee synchronisation, invitation roles, active sessions, database health, email logging, and content sanitisation.
Dependency injection makes those relationships visible. The constructor is a map of what the controller depends on, even when the map also reveals that a controller has become too broad.
View models are contracts
Entity Framework entities represent persistence. View models represent what a screen or endpoint needs. Keeping those concepts distinct reduces accidental over-posting, makes validation clearer, and prevents a database change from silently becoming a UI contract change.
For partial views and AJAX responses, the view model is also a client-side contract. Its shape determines what the replacement fragment can render.
Reuse patterns carefully
Shared partials and generated form fields can reduce duplication, but they need clear conventions. A reusable form component should document its assumptions about metadata, validation, labels, and edit/create differences.
Reuse is successful when it removes repeated decisions. It is harmful when it makes a simple feature impossible to understand without tracing several generic layers.
The lesson
Good boundaries are not about maximising the number of projects or classes. They are about making the direction of knowledge clear: HTTP concerns in controllers, reusable decisions in services, persistence in contexts and entities, and presentation contracts in view models and views.