Private space is identical to work profile. In the past, private space didn't exist and people used work profile instead as a workaround, but now that's not needed.

Private Space has a superior approach to isolation and encryption matching user profiles. Work profiles have some compromises for historical reasons. Private Space should be preferred over a work profile and the only reason to use a work profile for your own local usage is to use both a work profile and Private Space at the same time. Once GrapheneOS has support for multiple Private Spaces within a user, the use case for work profiles will be limited to the intended Bring Your Own Device enterprise deployment purpose. The intended purpose of work profiles is companies not having to give their employees work phones but rather owning/controlling a specific profile on their device with some influence over the overall device via rules for lock method, etc.