For my homelab: portable state. I don't use this image specifically but I use many others.

I put docker-compose files in ~/configdata/_docker/

The docker-compose files always mount volumes inside the ~/configdata/ directory. So let's say irssi has a config directory to mount I'd mount it to ~/configdata/irssi/config/

Then I can just run a daily backup on ~/configdata/ using duplicati or whatever differential backup tool of your choice and be able to restore application state, easily move it to another server, etc.

For software designed to run under your user account like irssi it's pretty much the same, look in ~/.config and ~/.local/share

Sure, this makes sense for a server, but irssi is a client. This is just a program running on your computer. You don't need a "homelab" or any nonsense like that.