Why is Thin controllers important in Laravel applications, and what problem does it solve for developers?

Why is Thin controllers important in Laravel applications, and what problem does it solve for developers? The key reason to understand thin controllers is that Laravel applications are usually composed of several layers that must work together predictably. Moving complex business logic into services or domain classes can keep controller methods easier to read and test. Ignoring that boundary can lead to duplicated logic, poor security, unnecessary database work, or code that is difficult to test. Why it matters in practice: Controllers group related request-handling logic and commonly coordinate validation, services, models, redirects, views and API responses. The specific focus here is thin controllers: Moving complex business logic into services or domain classes can keep controller methods easier to read and test. This question is designed to test not only terminology, but also how the concept fits into Laravel's request, application, database, security, or deployment workflow.