Selfhosted

No more dependency hell from one package needing libsomething.so 5.3.1 and another service absolutely can only run with libsomething.so 4.2.0

That and knowing that when i remove a container, its not leaving a bunch of cruft behind

You can also back up your compose file and data directories, pull the backup from another computer, and as long as the architecture is compatible you can just restore it with no problem. So basically, your services are a whole lot more portable. I recently did this when dedipath went under. Pulled my latest backup to a new server at virmach, and I was up and running as soon as the DNS propagated.

Modularity, compartmentalization, reliability, predictability.

One software needs MySQL 5, another needs mariadb 7. A third service needs PHP 7 while the distro supported version is 8. A fourth service uses cuda 11.7 - not 11.8 which is what everything in your package manager uses. a fifth service's install was only tested on latest Ubuntu, and now you need to figure out what rpm gives the exact library it expects. A sixth service expects odbc to be set up in a very specific way, but handwaves it in the installation docs. A seventh program expects a symlink at a specific place that is on the desktop version of the distro, but not the server version. And then you got that weird program that insist on admin access to the database so it can create it's own user. Since I don't trust it with that, let it just have it's own database server running in docker and good riddance.

And so on and so forth.. with docker not only is all this specified in excruciating details, it's also the exact same setup on every install.

You don't have it not working on arch because the maintainer of a library there decided to inline a patch that supposedly doesn't change anything, but somehow causes the program to segfault.

I can develop a service on windows, test it, deploy it to my Kubernetes cluster, and I don't even have to worry about which machine to deploy it on, it just runs it on a machine. Probably an Ubuntu machine, but maybe on that Gentoo node instead. And if my osx friend wants to try it out, then no problem. I can just give him a command, and it's running on his laptop. No worries about the right runtime or setting up environment or libraries and all that.

If you're an old Linux admin... This is what utopia looks like.

Edit: And restarting a container is almost like reinstalling the OS and the program. Since the image is static, restarting the container removes all file system cruft too and starts up a pristine new copy (of course except the specific files and folders you have chosen to save between restarts)