In India the Karandavyuha was one text among many. In Tibet it became foundational. It was translated in the imperial period, and the picture it gives, Avalokiteshvara as the being who has taken responsibility for a particular land and its people, was taken up as an account of Tibet itself. From that grew the identification of the emperor Songtsen Gampo, and later of the Dalai Lamas, as emanations of Avalokiteshvara, and the universal recitation of the six syllables by lay Tibetans, carved on stones, printed on flags and turned in prayer wheels. Few sutras have had so direct an effect on the self-understanding of a whole society.
It travelled east as well. A Chinese translation was made under the Song, and the mantra spread through East Asian Buddhism, though never with the saturation it reached in Tibet. The Princeton Dictionary of Buddhism notes the sutra chiefly for this: it is the scriptural source of the most recited mantra in the Buddhist world.
A caution about what the sutra is not. Its exalted Avalokiteshvara sits awkwardly with the Perfection of Wisdom literature, where the same bodhisattva teaches emptiness and where no formula has saving power in itself; the Heart Sutra's mantra is a summary of a teaching, not a key to a realm. Buddhist tradition has held the two together for a millennium and a half without much difficulty. A reader who meets only one of them will get a lopsided picture of what Avalokiteshvara means.