They were used as rat hunters in germany but now they're just companion dogs. I used to have one. He was an excellent little dog. They can become quite hyper and excited at times, and they have alot of energy...so don't think that just because they're small they can sit around the house all day. Mine was always on his feet and interested in doing something....ANYTHING.
They are smart little dogs as well, and just like agilitydobemom said, very loyal dogs. They have amazing character. I personally didn't find my dog to be snappy at all...he wasn't submissive though either. They like to challenge bigger dogs as they do have quite the fiesty little attitude. If you're looking for a dog, it all depends on your lifestyle, how you see yourself living in the future, and what you have in mind when you think of a dog.