From Roll Away the Stone by Israel Regardie:
The purpose of the hashish-session was simply to provide the student with a fore-taste or some adumbration of the mystical experience towards which he was focusing all his energies. It was never the intention of Crowley at any time to use drugs as a substitute for the body-mind discipline which he insisted on beyond all other things. This was the furthest notion from his mind. ...
I want to emphasize unequivocally that Crowley has asserted not once but a thousand times that the discipline itself was far more important than any one particular result or attainment. His thesis was that in training a concert pianist for example, one concentrates on drills, scales and exercises until enough manual dexterity and self-discipline has been developed by play Beethoven's Emperor Concerto. One does not start with the latter. It was in this area that he differs seriously from most of our contemporaries. ...
His fundamental premise was stated over and over again, in a hundred different ways. It was never that the drug experience per se could possibly replace the basic mental and spiritual discipline that he stood for, and which all occult teachers insisted upon. In fact, he was relatively certain that whatever the drug experience did evoke would soon be forgotten to become a cold, gray, vague memory. (pages 23 - 26)