Why block out number plates in photos?

[XABEBAGT]

Just curious as to why some people block out the number plates of their car when they post pictures. I guess they feel it makes them more secure but the reality is that your plates are on show when you drive your car around or when it is in a car show so does it really matter? Magazines and calenders almost never block number plates when they publish photos of cars. Personally, I have never considered it a problem to leave number plates uncovered but I do respect the decision of those who do. Just curious as to what benefit people perceive to gain from this exercise and has anyone ever had a problem caused by displaying their plates?
Cheers
Keith