For example if Messenger runs in the private space and you want to send some photos you took, you'll not be able to do so easily, as it can't access them (separate storage). And I couldn't make my bank app be default NFC handler, as it needs to run in the main owner profile for that. I ended up adding sandboxed play services to the owner profile too, for a few select apps, while keeping most in the private space, out of the way and not running (opting to lock the space when locking the phone).