That's what I do... mind you, I drive a Jeep with a soft top, so there's not a lot of security in locking to doors anyways, but I'd still rather have someone open the unlocked door and see that there's nothing worth taking than slash my canvas roof with a knife to try and get in (theives never take the time to realize the top is only zippered together...). It's all about perceived value in a vehicle... the more stuff that you have that "looks worth stealing" and the more effort you have to try and protect it, the worse off you end up. I always get laughs from friends because I leave $10 in coins sitting on the dash tray in my Jeep with the roof down in the middle of the city, and have never once had even a single coin go missing; I then bet somebody to leave a $5 bill there for a day and see how long it lasts.