When to use Final in PHP?

There is a nice article about “When to declare classes final”. A few quotes from it:

TL;DR: Make your classes always final, if they implement an interface, and no other public methods are defined

Why do I have to use final?

1. Preventing massive inheritance chain of doom
2. Encouraging composition
3. Force the developer to think about user public API
4. Force the developer to shrink an object’s public API
5. A final class can always be made extensible
6. extends breaks encapsulation
7. You don’t need that flexibility
8. You are free to change the code

When to avoid final:

Final classes only work effectively under following assumptions:

1. There is an abstraction (interface) that the final class implements
2. All of the public API of the final class is part of that interface

If one of these two pre-conditions is missing, then you will likely reach a point in time when you will make the class extensible, as your code is not truly relying on abstractions.

P.S. Thanks to @ocramius for great reading!