So I noticed yesterday that my home automation server (surprisingly useful when you have solar panels) was running out of storage space, and thought I was going to have to buy more.
Then I noticed that I'd stored every change in fan speed of the ventilation system for the past 18 months because I'd forgotten to add a retention policy.
Turns out I was storing multiple (10+) gigabytes of internal data from the ventilation system including fan speeds, system humidity and temperatures, etc as it is one of the most aggressively real time systems connected to the automation.
Oops?