A place to write down what worked, what broke, and what I would do differently next time.
Most of the value of a small server comes from the parts nobody touches. One package manager, one reverse proxy, one directory of static files. When something does go wrong, there is exactly one place to look, and that is usually worth more than any clever optimisation.
I have started writing before opening a terminal. Not because it is productive in any measurable way, but because the first hour is the only one where the list of things to do has not yet been rewritten by someone else's urgency.
A copy on the same disk is a convenience. A copy on a machine you can reach from the same account is a slightly larger convenience. Neither of them is a backup, and the difference only becomes obvious on the day it matters.