A use-case I can imagine is e.g. a password vault, a banking app, or a secure messaging app that you want isolated from everything. Even when running. And where "everything" includes infected apps, an infected host or even physical access.
Not sure if this architecture can handle that, nor of it's the best architecture to solve this problem, though.
Yes, yes, yes... those are all "legitimate" and likely good uses of this technology, but they're most likely just additional/bonus tertiary use cases to the main use case which motivated Google to expend effort on this feature: DRM.
It's much like how web browsers' incognito/private mode is really useful for web developers and certain kinds of troubleshooting, but those are tertiary uses to the primary consumer use case for which it was originally built: browsing porn without leaving history behind.
Not sure if this architecture can handle that, nor of it's the best architecture to solve this problem, though.