Check this article in the New York Times website about the dangers of hidden geotags in pictures you take - What the Internet Can See From Your Cat Pictures.
In a nutshell, if you take pictures of your cat with a smartphone that have geotagging enabled and post them on the Web, strangers can learn where you live by looking at the hidden geotags in the pictures. You can disable geotagging, or remove geotags from pictures before you post them online.