I installed Home Assistant to turn one lamp off at bedtime. That was the whole brief. Three weeks later I have a dashboard, a Zigbee coordinator, a presence sensor in the hallway and a notification that tells me when the tumble dryer has finished. The lamp, I should say, still does not turn off reliably.
This is the trap nobody warns you about properly. Home Assistant is not a product, it is a hobby disguised as a product. Every integration you add reveals two more you could add. I started with the lamp, which needed a Zigbee dongle, which needed me to learn the difference between Zigbee2MQTT and ZHA, which meant standing up an MQTT broker, which meant I now had Mosquitto running and felt obliged to put something else through it.
The automations are where the evenings really went. They look simple in the UI. Then you want one to fire only after sunset, but not if you are already asleep, but only if someone is actually home, and suddenly you are hand-editing automations.yaml and reading about templating and the template sensor and the difference between a state trigger and a numeric state trigger. I now have a folder of YAML that I genuinely could not reconstruct from memory, which is the homelab equivalent of a loft full of boxes you are afraid to open.
I run it in Docker on the same little box that does everything else, restart policy set to unless-stopped, config bind-mounted so I can back it up with everything else. That part, at least, I got right early, because I have learned the hard way that anything I will be sad to lose needs to be in a directory I am already backing up before I get attached to it.
Do I regret it? Not really. The dryer notification is genuinely good and I use it every day. But I went in to automate one lamp and came out with a second hobby, and if you are eyeing it up, go in with your eyes open. It will not stay small.