It is very seldom that someone asks this question. We generally grow up knowing only the 12 hour wristwatch. They might teach us the different methods to measure the passage of time and they might refer also to the 24 hour model. However, only a limited number of people knows that there exist 24 hour analog watches.
In reality, 24 hour watches not only exist but they are even fundamentals for certain people. Hence, before you buy your next watch it might be important to investigate whether you are more a 12 hour or 24 hour watch kind of person.