[red_admiral]

_Immutable_ data structures (not 100% the same thing, but a lot of overlap) avoid all kinds of concurrency problems, because you can safely pass them around and you'll never get a data race. You don't even need any locking (just to make things complicated, _lock-free_ data structures are another closely related but not identical concept).

Once you're running a distributed system, this kind of stuff comes into its own.

[taeric]

Careful with this wording. They avoid shared memory mutations. They don't necessarily change data races. Rather, they just change them since, by definition, every edit is now creating stale data.

At large, in distributed software, this is a distraction. Since most passing of messages around from one distributed piece to the other was already doing a copy across mediums. Such that sent data was already immutable from the senders perspective. (Granted, the preparation step can have you step on your own feet.)