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I guess, as a Scala enthusiast, it’s second nature to me - Scala incorporates immutable-by-default into its design so there are accommodations for it (.copy() methods on case classes, well-thought-out operators and methods on collections, “val” bindings, expression-oriented syntax).

It also lets you have normal OO classes and mutable vars anytime you want them, so you’re not stuck in a corner like you may sometimes be in Haskell if you don’t know the applicable FP pattern.

This helped me out quite a bit in a recent programming test for an employment screen – the challenge was to implement a time based key value store. One of the requirements that was revealed was that it needs to be able to back up and restore – this was as simple as storing the current root of the data in a list or map; it is effectively a snapshot.