It encourages a functional way of thinking, IMO: since you can't have mutable objects, use immutable data structures and functions which alter them, such that where you may have had:

    x.f(y)

you now have something like:

    x = f(x,y)

I've found that years of functional programming have mangled my brain. Now when I use something like Python, I only use dataclasses and accessor methods on them, or write methods which perform and return the result of some computation based on the values of the object.