Sat-Chit-Ananda represent infinite potentialities, unlimited in fact. Manifestation, in order to take place, needs to have definition created out of those infinite possibilities, and thereby specific finite choices brought to life. It is the role of the Supermind to effectuate this defining process.
The Supermind essentially turns potentiality into actual choices and thereby determines the forms, processes and actions of the manifestation. It turns the undifferentiated clay into a specific form of sculpture one could say. It turns random notes of music into a symphony. What we see in actual manifestation of forms is simply the specific details and choices that the Supermind has made at this time in this circumstance in this universe. It is not the only possible choice, simply because Sat-Chit-Ananda is unbounded and infinite and can thereby act as the foundation for any number of different forms of manifestation. Sri Aurobindo points out “The Infinite would not be the Infinite if it could not assume a manifold finiteness; the Absolute would not be the Absolute if it were denied in knowledge and power and will and manifestation of being a boundless capacity of self-determination.” The Supermind is the effective Knowledge-Will of the Infinite, which maintains its full awareness of the Infinite while choosing, defining and creating the world of finite forms.
reference: Sri Aurobindo, The Life Divine, Chapter 27, The Sevenfold Chord of Being