We only lock our house at night while we're all sleeping. Only out of paranoia, no one's ever been on my property at night (to my knowledge).
Tractors and small stuff get the keys left in them. All road-going vehicles get left unlocked, but the keys do come inside. Easy to find and use if someone wanted to try.
I have friends who live in the city come over to hang out or play outside, and they step out of their cars and then lock them with a beep as they walk towards me or the house. I can't help but ask "what the heck is wrong with you" each time. They usually just shrug and leave them locked.