Left my house in the East Midlands (U.K.) unoccupied and locked up for six year's. Of course turned off electricity at the consumer unit, mains gas at the meter and water at the stop tap. Left kitchen sink and bathroom taps on to drain cold water tank.
Couldn't get through the front door for post. No damp/mold and, amazingly, very little dust. There were piles of insects wrapped up by spiders in all corners. I've left the spiders and their webs alone because they're doing such a good job!