Speeding is brought up as an example that most replies refer to, but it really is not limited to that. How about jaywalking? Using the road on a bicycle when there's a bike lane available of varying quality? Or taking a piss in the bushes after a drunken night out? Downloading a 60 year old movie? Besides, perfect enforcement does not work with vague laws. It's not a world I would like to live in, where there is no room for error.