Reaching gnosis can result, for the religiously-oriented, in 'mystical experiences' - visitations by Gods, Demons, or the revealing of Divine Truths. For the magician however, the contents of such an experience are less interesting than what can be done with it - it is during moments of gnosis that sigils may be hurled; that the magician can reach through layers of space-time to manifest her will, and Gods can possess their devotees. Historically, many of the techniques of gnosis have been augmented by the use of drugs - from witches' flying ointments to the LSD & sensory deprivation experiments of John Lilly.
Any system or tradition is incomplete whilst it remains a theoretical curiosity. Study alone is of little value, unless it is complemented by practical messing about. Whole volumes might be written 'explaining' the magical natures of the various entities such as Goddesses, Demons, or Spirits, but these are no substitute for the experienced 'reality' of a deity during the course of a ritual. Although there is much talk of 'magical secrets', the only 'true' secrets are those which can be personally discovered through the light of direct magical experience.
Altered states of Consciousness may be achieved using a combination of internal changes (the use of the methods of gnosis), and interactions with others, as in hypnosis, group ritual, or orgia.