[kevinavery]

Also referred to in this context as encapsulation. OOP provides a method of information hiding that allows implementation details to be changed later without changing the public API.

[abiox]

one downside being that you risk creating obscured islands of mutable state, complecting engineering efforts.

[kevinavery]

I view that more as a risk of using mutable state, not OOP. Regardless, I'd rather have the mutable state contained in as limited a scope as possible.