A construction ship was a low-impulse vessel used for deploying and controlling worker bees, which operated as a team in order to construct starbases and other large-scale facilities. They were also equipped with tractor beams. When available in excess, the construction ships were charged with towing disabled vessels to berth for repair.
A capture of an alien race's construction vessels could provide its captor with the technical data necessary to construct alien facilities. Example: a Federation fleet in possession of a Borg construction ship would become capable of building Borg facilities and vessels, and other technologies. This also applies when the Federation has captured other alien races construction ships. (TNG video games: Armada, Armada II)