Locutus of Borg

The Borg intended to use Picard as an intermediary, a spokesman for the Human race in order to facilitate the assimilation of Earth so that the process would be as quick and efficient (or as perfect, from the perspective of the Borg Collective) as possible, with the fewest number of casualties on both sides.

Picard's assimilation allowed the Borg to acquire the whole of his knowledge and experience, as well as his own personal knowledge (a fact that was made apparent when Locutus addressed Commander Riker as "Number one").