At that level it's similar tradeoffs. Consider what the code would look like if it were purely functional. In fact a good answer to your question would be for a

At that level it's similar tradeoffs. Consider what the code would look like if it were purely functional. In fact a good answer to your question would be for a thought exercise take a look at how XMonad is implemented in Haskell. That would be a completely different approach to the large, heavily coupled messes that OOP can sometimes lead to when modeling the state as mutable object members.