Starting girl and "Origin override"

I find the way this is presented to be really unintuitive, so I'm hoping to understand what the goal here is.

At this point, it's a toggle that determines if App.StartingGirls.applyPlayerOrigin() is run on passage refresh. That function sets origin, custom.tattoo, and (rarely) pregSource.

I would be interested in just running the function directly when activeSlave is set, or not running it as the case may be. Is there some use case I am missing?