Why YSK: There are a lot of people these days living alone with pets and if anything happened to the owner, others may not know to attend to the pet. If something happened to you, a coma, an accident, death, etc, your wallet would be the first place anyone would look for info about you and it would probably be the fastest way to bring attention to your small loved ones.
This seems like a good idea for all pet owners. My family and friends would think of my pets eventually, but it might not be the first thing on their minds.