[chowells]

Local mutability is fantastic and practical... In a language like Haskell where the type system tracks exactly what values are mutable and all mutation is precisely scoped by functions that freeze the value they generate in a way that prevents leaking.

In a language that isn't so precise, it's a lot harder to get value from the idea.

[Tainnor]

You can get value out of local mutability in languages like Scala or Kotlin. Variables can be declared mutable in the scope of a function, and their value can then later be assigned to a non-mutable variable, for example. Collections also come in mutable and immutable variants (although this has some pitfalls in Kotlin).