Thank you for the brief list!
To further some advantages, here are some I can think of:
- Safer app installation and updating process, as dependency hell is much more unlikely to happen (or probably even impossible)
- malcontent (parental control) support
- Rootless and user installs
- Configure the sandbox a bit more conveniently, as opposed to Firejail, or even bubblewrap directly
- No need to create a new desktop entry if you need to persistently set environment variables, socket, etc. strictly for a specific app (except Electron)
And to complete with a disadvantage:
- Strong dependency to XDG portals. If a portal doesn’t exist for a specific use case, then you’re out of luck, as you have to rely on static permissions, or can’t do anything about it.