Portals and Sandboxes - use cases?

[Zach Villers]

Hi, I'm reading through flatpak developer docs and came across info
about portals and sandboxing in the developer wiki.
https://github.com/flatpak/flatpak/wiki

I'm trying to understand the use cases and have been trying to walk
through examples in my head. 

I've edited a text file in a flatpak'd Gedit, I save the file, which
saves to $HOME/.var/app/$APPID. I decide I need to do some last minute
text transformations before emailing it off, and want to just run
/usr/bin/sed in place over the file. Since I am running sed  as the same
user, I should be able to access the app data in my home directory,
correct? If I want send the file via an email using a webmail client,
would I be able to authorize Gedit to attach the file to my webmail
client?

Would I also be able to copy the file to a remote host using scp from
the remote machine?

Would I also be able to authorize a back-up application to have access
to all of my user data in sandboxed applications? How do I restore user
data to the correct places from, say duply/duplicity?

Apologies if these are obvious from the documentation.

Thanks,

-- 
  Zach Villers
  zach at znix.site