Guardians of the Galaxy Vol. 2 Spoilers ahead.
May be I wasn't paying enough attention. Thus, miss the plot. So Ego wanted to find a person or a entity, who would carry the energy that he needed in order to spread the light of Ego's planet everywhere. Right ? That's why he spread some seed like thing everywhere in the universe.
But why? I mean what was the big plan? Was he wanted to kill all life but himself / itself? If not then why destroying only habitable planets? He could have use any planet without life to spread the Ego planet's branch.