After experimenting and using them a little, I have become a big fan of the guest access tokens, especially because I can let the guest access expire.
A good friend of mine is not into technology at all, but she can click links. And now I just have to send her a link in an encrypted message to allow her access to photos or other files. She doesn't have to sign up to hubzilla.
I can also make posts with non-public pictures and files accessible to Diaspora or friendica users by posting the link in a limited post.
Of course, it is no sensible solution for very sensitive information. With the tokens expiring it is still a reasonably high level of privacy for most purposes.