Docker is great for making sure that magic bash script that brings the system up actually works again on someone else’s computer or after a big upgrade on your dev machine or whatever.

So many custom build scripts I’ve run into over the years have some kind of unstated dependency on the initial system they were written on, or explicit dependencies on something tricky to install, and as such are really annoying to diagnose later on, especially if they make significant system changes.

Docker is strictly better than a folder full of bash scripts and a Readme.txt. I would have loved having it when I had to operate servers like that with tons of websites running on them. So much nicer to be able to manage dependency upgrades per-site rather than server-wide, invariably causing something to quietly break on one of 200 sites.