The aim of Yoga and Sāṃkhya is to be yoked to the more discerning aspects of the psyche, rather than just to the more grasping aspects of the psyche.
In the former the tendency of the Buddhi to discern discriminately dominates the tendency of Ahaṃkāra to grasp indiscriminately. In the latter the tendency of the Ahaṃkāra to grasp dominates the tendency of the Buddhi to discern.
The former is a state known as Buddhi Sattva where the clarity of discernment dominates the indiscriminate grasping nature of the Ahaṃkāra. The latter is a state of Buddhi Tamas, where the discerning qualities of the Buddhi are obscured by the grasping nature of the Ahaṃkāra.
Thus our Yoga Sādhana has but one aim, that of the reduction of the obscuration of Tamas (apart from deep sleep) in the Buddhi. This reduction of Tamas facilitates the ascent of the clarity of Sattva, as in the metaphor of the reduction of the cloud facilitates the ascent of the sun discussed within yesterdays post.