Any scenario where you have to atomically update 2 actors. To use a simple analogy for illustrative purposes, transferring money between 2 accounts, you need to lock both actors before incrementing/decrementing. Because in the real world, the accounts can change from other pending parallel transactions and edits. Handshakes are very error prone. Lock the actor, do the critical transaction, unlock.

In a rationale world, this works. In a prejudiced world, devs fight against locks in actor models.

Hence why I had to roll my own …