Save time and money by collaborating
Choosing composition over inheritance may weaken encapsulation
These functions tap really well in to the weakly typed and procedural side of PHP. If you've already been riding the wave of modern PHP for a while, you've learned to hate that side of PHP.
Make your code more testable, maintainable and configurable
There's always risks when using third party code.
Make interaction with your objects explicit
Writing setter methods is a sure way to invite confusion and instability to the codebase. Read on how to get rid of them!
Demand clear answers from your objects, don't accept mumbling