Is this an advantage?

well, building stuff with flatpak is not THAT intuitive. no package format before docker was from my point of view. on the other side, packaging also cleans up and docker-insides often are not cleaned up :D

depends on your use case. I wanted a way of removing network access for my text editors and starting ephermal firefox instances that are completely independent from each other. Its just an easier way to hack around an application tbh.

I'm thinking of how this could be used on Windows systems.

But honestly it's just really cool.