Why does Yogi perform actions?

Kayena manasa budhya kevalaih indriye api |

Yoginaha karma kurvanthi sangam thyaktwa atmashuddgaye || 5.11 ||

Meaning:

"YOGIS, having abandoned attachment, perform actions merely by the body, mind, intellect and senses, for the purification of the self (ego) ."

My understanding:

One who is practicing Karma-Yoga, does actions only for purification of self/ego. Even though he is performing action, his attachments with the actions, world, body, intellect and mind are complitely vanished, by having full awareness that is Sakshi. But still he might having ego of knowing everything. Thus he is doing actions, to come out of this ego also.

Commentary by Chinmayananda Swami:

A Karma-YogiN's attempt is to keep himself within himself --- as a detached but interested observer of all that is happening around and within himself. When he thus observes himself, from within himself, as a worker in any given field, it becomes easy for him to see that all actions belong to the above-mentioned instruments-of-action and not to the detached OBSERVER in him. Here, however, he must realise that the OBSERVER in himself is not the Truth, but this OBSERVER is "Truth standing on the open balcony of the intellect." Even while thus observing ourselves in action, we are ever conscious of the very OBSERVER in ourselves. "The Consciousness that illumines the very OBSERVER, is the Spiritual-centre, the Self," is the declaration of all Upanishads.

If thus, the Spiritual-centre itself is something beyond the "observer," why should a Karma-Yogin practise this technique of self-observation called in our Shastras the "witness-attitude" (Sakshibhava)? This is answered at the end of the verse when Bhagavan says, "for the purification of the ego." By such a practice, the seeker will be entering into the field of activity and pursuing the work without the self-arrogating ego, thereby rendering himself available for an easy and effective purgation of the existing vasana-impurities. To the degree these are removed, to that degree the inner equipments become clearer and steadier, rendering the reflection of the Divine-Consciousness in them more and more vivid.