For me it's the risk of not knowing what I'm doing, practice management wise or dentistry wise, and failing. It's an unnecessary risk. Also I want to be mentored by a great person for a few years, and if I'm the owner that opportunity is not there. Also, you don't know the style of practice that you want to lead. Different practices are vastly different in terms of scheduling, armamentarium, etc.. you should try a few different styles and then decide which aspects of which practices you like. Just my few cents.