I thought an example of a private space is the lounge and other restricted categories.
The lounge here is like an airline lounge that you can access at Trust Level 3 (TL3):
access a private “frequent flier’s lounge” category only visible to users at trust level 3 and higher
https://meta.discourse.org/t/what-do-user-trust-levels-do/4924/6?u=remah