Every time you save a change to an assistant (a new personality, an edited greeting, a swapped voice, updated instructions, and more), Sulus keeps a snapshot of the assistant as it existed before that change. Version History is where those snapshots live. It lets you see exactly what changed and when, and roll an assistant back to an earlier state without having to remember or manually redo every setting by hand.
This is the safety net for any change you make to an assistant. For example, if you changed your assistant's voice using the steps in How to Change Your Voice Assistant's Voice and decide you liked the previous voice better, you don't need to reopen the Personality dropdown or Advanced Editor and hunt for the old voice. You can restore the version from just before you made the change instead.