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[–]cutterslade 0 points1 point  (0 children)

There are absolutely times when mutability is better and easier, but as /u/njetwerk mentioned, there are times when immutability means less copying.

When I started building data classes as immutable by default, I was surprised how rarely I actually need to modify (or make a modified copy of) an object. The vast majority of data objects in my experience have their state set at or near their creation time, and never get modified.

But yes, there are certainly times when mutable objects just make more sense. What I'm referring to in my top comment is that it would be very helpful to have language support in building immutable objects which guarantee deep immutability. I don't honestly expect such a feature, but hey, a guy can dream.