[Diggsey]

Actors are generally a very powerful abstraction.

To give a specific example: they can be used to mediate access to a resource without requiring complex synchronisation: instead of sharing a piece of mutable state (like a cache) and protecting it with a lock, you can ensure a single actor accesses the cache, and other code communicates with that actor.

This is particularly useful with asynchronous code, because it's not possible to have a fair, asynchronous "passive" mutex without suffering from the thundering-herd problem. If you try to implement such a mutex, you will find yourself needing to queue up lock requests and responses, and you will end up reinventing the concept of an actor.