They provide privacy while you learn. Students are less intimidated in a one to one learning situation.
Private lessons are the quickest way to become an accomplished dancer.
Group classes provide practice time dancing. The knowledge you acquire in your private lessons will be re- enforced and made stronger in your group classes. In group classes you can meet other many students in the studio. These semi - private lessons are almost like private, but you share the cost. Some people learn easily in groups, while others need the benefits of private instruction.