Why does ISP simplify refactoring?

ISP simplifies refactoring because segregated, small interfaces create local zones of change and eliminate the cascading modifications that typically arise when working with "fat" interfaces.

In detail:

#1. Fewer places that need to change

When an interface is small and specialized, changing it only affects the implementations that actually use that contract. A "fat" interface means dozens of dependent classes, so one modified method breaks the whole project.

#2. A more transparent architecture

Small interfaces reflect clear roles ("prints", "scans", "logs"). During refactoring it is easy to identify which part of the system is responsible for what. With "fat" interfaces you have to work out which part relates to which responsibility.

#3. Easier to reuse and swap implementations

If an interface is small, one implementation can easily be replaced with another without breaking client code. This is especially important when refactoring the architecture or extracting functionality into separate services.

#4. Avoiding unnecessary functionality in classes

When a class implements only the interfaces it needs, there is no "extra" code inside it. This reduces the chance of errors when it is rewritten.

#5. Localization of changes

Small interfaces mean that a change in one functional area does not affect another. For example, a change to logging should not change the interface and classes responsible for the network API.

#6. Stable contracts

If an interface is too large, it changes often, because every team or feature affects it. When interfaces are small, they are more stable, and stable contracts are the foundation of safe refactoring.

#7. Simplifies decomposition when moving to microservices or modules

Segregated interfaces are easier to extract into separate modules - each responsible for its own "micro-function".

Summary: ISP simplifies refactoring because it reduces the scope of changes, makes the architecture clearer, reduces coupled dependencies, and allows parts of the system to be changed in isolation without touching the whole project.