This old but good thread at the FDD community site discusses how effective class ownership can be. I particularly liked this comment from Jeff De Luca.

If you do not use class ownership, when you assign a feature to someone then they must touch four classes (for example) in the system. They must have knowledge of four classes in the system. Think of very high use classes - such as LoanApplication in a Lending system. There would be a class with dozens of methods and attributes each written by a different person at a different date and time!!! (if not using class ownership)

Encapsulation is one of the founding principles of objects and is about a class being able to hide how it does what it does, and vary how it does what it does as long as it preserves its interface to all other objects. Well, class ownership naturally fits this fundamental requirement of objects. With class ownership you get better consistency of implementation and better consistency of interface.