It depends on what kind of development you're doing. For most web and business programming I've done, at the end of the day I'm mostly just taking data and tra

It depends on what kind of development you're doing. For most web and business programming I've done, at the end of the day I'm mostly just taking data and transforming it into other data. Most of the time, looking at these programs as a series of functions through which data gets piped to obtain the result works well. As a result I think that functional programming is a good fit a ton of code that is written using OOP. For fun, I tried converting some old side projects to F#. Once I'd gotten used to the language, I ended up being able to express the same ideas more clearly, and with fewer lines of code. Functional programming isn't magic, but it can be very effective when used in the right places. Lately, I've been getting into game development as a hobby. And when I'm simulating a miniature world with hundreds or thousands of stateful actors, I find that OOP works really well - in that the way to code models the game world aligns well with my mental model of the game world. You absolutely can program games using a functional style - I've just found OOP to be a better fit here for my uses. It's still useful to use a functional approach where you can, though, even inside an OOP game code base. John Carmack has written and spoken about this.