This spice must follow certain rules though. The melody must be singable. The voices should move with variety and semi-independence from one another, otherwise its not countering a point. The music must fit the text. Happy words get happy shiny music, sad words don't.
Dissonance is used to connect consonances.
And it need not start at the same time, suggestion more advanced contrapuntal techniques such as fugues. When entrances are temporally displaced they often don't start on a Perfect interval. Variety is achieved by not using parallel intervals. To repeat a perfect consonance would be like attempting to repeat perfection. Zarlino exercises himself quite a bit in his attempt to give an account why consecutive imperfect intervals of the same size should be avoided.