When the yogi finds that yoga is inadequate and useless to realize the 'Self' must drop yoga and take up the path of Gnana.+

Yoga has its place rather than its value and its value is for a certain type of mindset. 

Sage Sankara said:- Neither by the practice of yoga nor philosophy, nor by good works nor by learning, does liberation come, but only through the realization that Atman and Brahman are one in no other way. (1) Vivekachoodamani v 56, pg. 25

Lord Krishna confesses that the oldest wisdom of India (our true Advaitic wisdom) has been lost: people misinterpret and falsify it today as they did then. It is not yoga but the philosophic truth. But nobody knows it. The teachers of philosophy and leaders of mysticism or religion do not want to inquire into truth and have no time for it. (Gita –Chap- IV-v.2) 

In Gita Chap.IV where Lord Krishna says: ~ "This yoga has been lost for ages" The word yoga refers to Gnana yoga, not other yogas: the force of the word this is to point this out. 

Lord Krishna describes some of the other yogas but devotes this chapter separately to Gnana Yoga. So one sees even in those ancient days people did not care for Advaita; they wanted religion; hence, Gnana got lost. That is why Krishna calls it "the supreme secret." Krishna points out that yoga must see "Brahman in action." 

Gita Chap.IV: "He who achieves perfection in Yoga finds the Self in time." This means that after his yoga is finished, he begins the inquiry into ultimate truth, and in due course, this inquiry produces the realization of the universal Spirit as the result. 

When the yogi finds that yoga is inadequate and useless to realize the 'Self' must drop yoga and take up the path of Gnana. 

Lord Krishna Says Ch. V:~ “Those who know the ‘Self’ in truth.". The last two words (tattvataha) are usually ignored by pundits, but they make all the difference between the ordinary concept of God and the truth about God. 

Sage Sankara says: - Yoga is not the means of liberation (page 132-133 - Commentary on Brhadaranyakopanishad.

In Sutra Bashya and Manduka: - The Samadhi and sleep are identical. 

Brihad Upanishad: does not advocate Samadhi.

Sage Sankara in the commentary to "Brahma Sutras:- " "The highest beatitude is not to be attained by Yoga." (Sacred Books of East Series page 298 Vol.1.) he also says Samadhi is the same as sleep (p.312) ---which indicates that yoga is not the means to Self-realization. And yogic Samadhi is not nondual Self-awareness. 

Panchadasi: - the impossibility of yoga arrives at a successful end to its practices. (P.509 v, 109)

Remember:~

Yoga will remove restlessness and help to get receptiveness, but never Truth because it ignores the external world. 

Yoga cannot remove ignorance. It is only a step. It removes obstructions.

Yoga can yield only the duality because everything that one can do or practice becomes a vanishing 'known.' It yields the relative truth, i.e. true from a particular viewpoint, not the ultimate truth.

Yoga implies duality! Yoga means joining two things, something to which the yogi is to be joined. He thinks I want to know God, I want to attain Union. So he has the ego and cannot attain it, whereas the first thing in the path of truth is to question the ‘I’ until its illusory nature is perceived and the seeker no longer says "I want to attain ultimate truth.

One has nothing to get for the Self, as it has vanished on inquiry, not even will he say I will work for the sake the humanity.

It is not possible to stop the thoughts for more than a half-second whilst in the waking experience. If one succeeds in controlling thought and then banishes it, one passes into Nirvikalpa Samadhi, which is identical with deep sleep. The only difference between ordinary deep sleep and Samadhi, therefore, is that the ordinary man falls asleep involuntarily whereas the yogi has the satisfaction of knowing that he has passed into sleep by his own effort of will in banishing thoughts.

Sage Patanjali warns against sleep as a hindrance to yoga, he means when it occurs in the early stages of the practice before one has obtained the power of control and consequently to banish the thought. This fact that Samadhi is deep sleep is kept secret because people would not be tempted to take up yoga. Then what is the value of it? Why, to sharpen the mind, to enable it to keep away all extraneous thoughts when one gets out to reason in the practice of the next higher stage, i.e. Gnana.:~Santthosh Kumaar