Sri Aurobindo
Letters of Sri Aurobindo
Volume I - Part 5
You take a very utilitarian view of spiritual things. Whatever develops in the sadhana, provided it is genuine, has its place in 
the total experience and knowledge. A knowledge of the occult worlds and occult forces and phenomena has its place also. Visions and voices are only a small part of that vast realm of occult experience. As for utility, for one who has intelligence and discrimination, visions etc. have many uses – but very little use for those who have no discrimination or understanding.