For the meditation on the nature of your own mind it is customary to ask your teacher for pointing-out instructions. Some practitioners are lucky enough to realize their true nature of mind straight away, whereas others merely perceive a sensation of it, a certain experience of the true nature of mind. But if they don't know exactly how mind and the consciousnesses function, their experience will dissolve after a few days. The understanding of mind and the eight kinds of consciousness is obtained through the highest understanding (Skt. “prajna”) of listening and reflecting. When we really meditate on this basis and glimpse the true nature of mind, we will be able to steadily increase our experience of it through all subsequent meditation. That’s why it is extremely useful to know about the eight kinds of consciousness.
—from Luminous Heart: The Third Karmapa on Consciousness, Wisdom, and Buddha Nature, translated and introduced by Karl Brunnhölzl