Hatha Yoga’s stated purpose is to prepare the practitioner for higher meditative practices. The practices of Hatha Yoga are meant to “purify” the practitioner and enhance Prana or life force.
How do you know you are cleansed enough?
Yoga Sūtras offer couple of ways to assess this.
Sūtra 2.40 | śauchāt svāṅga jugupsā paraiḥ asaṁsargah
From purification, aversion develops towards one’s own body and this attitude extends towards contact with other bodies.
Why aversion? Because there is no end to cleansing. If you think otherwise, try not brushing your teeth for a day and see if decades of Hatha Yoga will be of help. In spite of all the work, the body gets “dirty” easily and has to be cleaned again and again. This Sysiphusian task creates in a Yogi an attitude of aversion or indifference to his own body. Now, why would a Yogi risk contact with another body?!
However, cleanliness is not limited to the physical body. The practices are also meant to cleanse the mind to make it conducive to the practice of Yoga.
Sūtra 2.41 | sattva śuddhi saumanasya ekāgraya indriya jaya ātmadarśana yogyatvāni ca
The result of internal cleanliness is a mind that is full of clarity and tranquility; that is focussed and has control over the sense organs. Such a mind becomes fit for practice of Yoga.
A serious practitioner of Hatha Yoga should regularly recollect these Sūtras to see if he is on the right direction.