I have an arduino project where it may only run a couple times (10 mins) a month for years. Can it stay plugged in or do I need to trigger a timer?
Well its wasting electricity to run it unnecessarily, but there's no technical reason to avoid it... The electrolytic capacitors might age somewhat over the years but they do that anyway. The sketch could fade from the microcontroller's flash memory after a decade or two and need reprogramming!