I don’t have any experience with snaps so this is all new to me. Snaps install software at a system level right? Why on earth would there be anything in a user home directory? What if you have multiple users? Does snap get confused?
Snaps run out of a squashfs partition, but the app may save app config in the user's home directory (if they request the HOME interface, I believe).
After fighting with node, vlc and ffmpeg snaps not working reliably, I had to add a warning for my PhotoStructure users on Ubuntu to avoid those packages (and how to install them via apt).
I agree with a bunch of people here: snap promises some great features, but in practice the horrible performance, additional resource consumption, and spotty reliability led to me actively avoiding snap packages and looking for an alternative installation.
Snap stores user-specific application data in /home/user/snap/ folder. Like when packaged application wants to write into $HOME, snap gives it some sub-folder inside /home/user/snap.
Ah ok I understand now. Sibling comments reference the MacOS Library and *NIX ~/.local approaches. Both of those seem to make a lot more sense. Is there a config for Snaps to store user data in a different path, like ~/.local/snap/?
No; they use some magic with security policies and mounts so $HOME/snap is hard coded. Some of the early comments in that "4 year old bug" linked here explain it.
Most likely they download some things when you first run the software. This pretty common but usually opaque to the user due to it being in .local or .cache.
