hi
thieves often slash the side of curtainsiders to see what booty they can steal.
leaving the doors open saves them the trouble (and an expensive repair bill for the haulier)
i can see your point re the ones that are left closed however high value loads arent usually left in laybys or insecure parking areas anyway.
the reason for parking skew wiff or jackknifed as you say is to prevent the cabs mirrors being struck by a vehicle travelling too close to the side of the road preventing another expensive repair bill! especially if the other vehicle doesnt stop to give his details.
hope this helps
baz



