That was interseting to hear.
The benefits are to be seen provided the mantras are incanted in the right way...right tone, inflection and meter.dream I can give example of one mantra that was given to me in a dream. I used it to vaporize some "inner demons"... Of course you know that I say this in the symbolic way. Moreover, it helps me relax when i dont have time to meditate and connects me with the unknown teacher who came to me in a dream and gave me the mantra. I got it when my life was in doldrums and it helped me stay sane and practically saved my life.
I so agree with the right incantations (again unless there is massive devotion towards diety which has incredible potential),otherwise it is waste of time.
A sadhu minding his gurus ashram next door to where I spent a couple of months at friends hermitage was doing his sadhana which included his guru mantra and not sure if he did anything else (IMO he must have been in one way or another).
Anyway they came over one day to ask the hermitess I stayed with for help as the sadhu went blind (!) during sadhana. His guru returned in few days time and helped him to gain his vision back after period of some days.
We suspect that it was either some wierd combo of sadhana or something not done in a proper way.
Or what my friend reckons that he might have been doing datura , as many sadhus do in Himalayas. Dont know why would that get him blind though personally.