For sedentary individuals, taking up dance as a hobby or a past time can undoubtably have a positive effect on their overall health, fitness and well being, just as taking up any physical discipline can have a positive effect. Movements such as Zumba, aerobics, Jazzercise etc are all forms of dance fitness; as well as the plethora of community dance classes across a range of disciplines. While great at getting otherwise sedentary individuals into physical exercise, dance fitness has no relevance to the dance professional.
As far as physical fitness goes, for the professional (or preprofessional) dancer, dance training alone is not enough. If you are serious about your dance performance you should get fit in order to dance, not dance to get fit. This means training outwith your technique and performance classes, to prepare the body for the demands you throw at it. Strength, aerobic, interval, plyometric and flexibility training are all necessary in order to condition your body to perform at the highest level.
Every professional athlete and sportsman/woman will train not only in their discipline, but for their discipline. A sprinter does not only sprint in their training sessions, a golfer does not spend all their time swinging clubs and a dancer should not spend all their time working on repetoire and syllabus.