My greatest lifesaver so far is a set of ansible scripts that will completely reinstall my desktop, servers, VMs and Raspberries to the settings and packages I want. I tend to break things while experimenting and I'm a lazy bastard when it comes to backups, so this tiny bit of organisation keeps me sane.

Last week one of my servers went unresponsive and subsequently got corrupted by a hard reset, five minutes later I was up and running again. That makes keeping my /etc files in a git repo worth it.
I sleep soundly knowing my crontab kicks off the right jobs on my hadoop clusters every five minutes without me having to manually check /etc after an upgrade.

The other thing is the reason I have two hadoop clusters: I got fed up using google to (not) find the things I need to develop stuff, so I've been busy building a search engine specifically for developer resources. The more time I spend building it, the more it proves that I really need something better than google.

Might turn out to be overkill, might be better than sliced bread.