I've got nothing against downloading things only once - I have a few dozens of VM at home. But once you reach a certain point maintaining offline ISOs for updating can become a chore, and larger ISOs take longer to write to flash install media by nature. Once you get a big enough network, homogenizing to a single distro can become problematic: some software just works better on certain distros.

I'll admit that I did miss the point of this post initially wondering why there was a post about downloading Debian when their website was pretty straightforward - the title caught me off guard and doesn't quite match what it really is on the inside. Inside is much much more involved than a simple download.

Therein lies the wrinkle: there's a wide spectrum of selfhosters on this community, everyone from people getting their first VM server online with a bit of scripted container magic, all the way to senior+ IT and software engineers who can write GUI front ends to make Linux a router. (source: skimming the community first page). For a lot of folks, re-downloading every time is an ok middle ground because it just works, and they're counting on the internet existing in general to remotely access their gear once it's deployed.

Not everyone is going to always pick the ""best"" or ""most efficient"" route every time because in my experience as a professional IT engineer, people tend towards the easy solution because it's straightforward. And from a security perspective, I'm just happy if people choose to update their servers regularly. I'd rather see them inefficient but secure than efficient and out of date every cycle.

At home, I use a personal package mirror for that. It has the benefit of also running periodic replications on schedule* to be available as a target that auto updates work from. Bit harder to set up than a single offline ISO, but once it's up it's fairly low maintenance. Off-hand, I think I keep around a few versions each of Ubuntu, Debian, Rocky, Alma, EPEL, Cygwin, Xen, and Proxmox. A representative set of most of my network where I have either three or more nodes of a given OS, or that OS is on a network where Internet access is blocked (such as my management network). vCenter serves as its own mirror for my ESXi hosts, and I use Gitea as a docker repo and CI/CD.

I also have a library of ISOs on an SMB share sorted by distro and architecture. These are generally the net install versions or the DVD versions that get the OS installed enough to use a package repo.

I've worked on full air gap systems before, and those can be just a chore in general. ISO update sometimes can be the best way, because everything else is blocked on the firewall.

*Before anyone corrects me, yes I am aware you can set up something similar to generate ISOs