I have only tried FP a little bit, but I personally found value in non mutating data and removing side effects, even in the portions of my code that are OO. It

I have only tried FP a little bit, but I personally found value in non mutating data and removing side effects, even in the portions of my code that are OO. It's refreshing getting rid of the whole class of bugs caused by developers using harmless sounding method names that subtly alter their data. It did require substantial rewriting of the basic units of the program I tried it in, so there is that...