Unless it's enforced, a rule or law isn't really important, rite?

I've been hearing about rules and laws that are supposedly on the books, but they're almost never enforced... so are they really important? Examples, I've heard that (in my area at the time) children under 13 weren't allowed to stay home alone... we're not allowed to travel with people in the back of pick-up bed, playing poker or gambling with money, age limits for certain things (like playing on a game machine)