A group act compares more closely to a Duo Act than a Solo Act or Duo act; it's choreography is largely redundant.

While a solo act may have a move mirrored between two performers, a group act mirrors them multiple times. As such, the choreography is easier to expand to a unknown count of individuals.

This usually useful in school or training environments. Participants may not be ready for the scrutiny of a smaller act - though experience and ability can vary widely in a group.