There are a lot of ways that a dental practice needs to be "mobile". Whether it's a dentist hitting the road to visit schools, daycare centers, or even workplaces (a dentist who comes to me? Yes please!) or a hygienist with a regular rotation of offices, moving around that much means you need to have access on the road.
Additionally, many practices have more than one site—or would like to grow in that direction. No matter how your practice is set up, many can benefit from software that isn't only accessible in one office at a time.