When you're in a branching possibility space with undo, experimentation is cheap.

It encourages exploration, experimentation, and discovery.

But most branching UIs hit you over the head with it; it consumes all x/y space.

All of that choice and state can be overwhelming!

Constantly reminding you that you're awash in a sea of options.

You want a subtle reminder that you're in a branching space and can undo anything and experimentation is OK... without intimidating you with the dizzying freedom of infinite choice.