Wow, I'm surprised this thread got so many replies!
Regarding Psychedelic Therapy, please be aware that this method involves very little interaction between the person who trips and the therapist. Such interaction is much more intense in psycholitic therapy. In psycholitic therapy the patient is given low to moderate dosages of LSD, and there's lots of interaction with the therapist, who may or may not take LSD himself. There have also been psycholitic group sessions. Stan Grof and others have come to the conclusion that although both approaches can be useful, depending on the condition of the patient, the high dose Psychedelic Therapy is less time-consuming and very often much more effective.
Also it should be noted that from Stan Grof's point of view, it seems everyone who has gone through the process of being born could benefit from a properly conducted LSD session. This of course includes the children already mentioned by GOD.
Grof also conducted sessions for artists, philosophers and (religious) scholars. Though these people didn't "need" therapy, they were still guided through the experience by therapists.
What a therapist or sitter does during a Psychedelic Therapy session is taking full responsibility for the physical and psychological safety of the person undergoing the experience, so that the person can focus fully on what occurs within, and surrender to it all.
As GOD and Brugmansia have illustrated it's quite possible to do a high dose without a sitter, and indeed for people who are not in need of therapy there may also not be as much of a need for one, especially if they know what to expect and what they want to achieve (intent, purpose). But it seems from this book and the other LSD manual I read recently that even the best psychonauts could achieve more benefit if there's a trusted, sober person nearby.
Magickmumu, I think when a shaman is guiding an entire group, and that shaman is the only sitter around, he cannot possibly take care of all the participants on a personal level. He can only provide everyone with a particular thing to focus on, like music. If he would give the participants a dose that is as psychologically jarring as 500 ug of LSD, he would no longer be capable of taking care of everyone, at least not directly, especially if he had taken a similar dose himself. Such settings are great for experienced (or religious) users, but not for people who really need intense guidance. Also: the shaman must be extremely qualified and dedicated, otherwise he or she should not conduct group sessions.
Ahuaeynjxs, welcome back! Regarding the electricity, that's very difficult. I agree it would be desirable, but kind of impractical. It would mean no music, no isolation tank, and no refrigerated drinks... I think the benefits of music and perhaps spending some time in an isolation tank outweigh the negative effects of electrosmog.
Stan Grof often stresses that though the first 4 or 5 hours of the experience should be spent in a reclining position with headphones and a blindfold on, it can be of tremendous benefit to go into nature during the concluding stages. Therefore the ideal location for psychedelic treatment centers would be in a natural environment, preferably close to a lake, river or ocean. I remember leaving the darkness of my room towards the end my last (medium dose) LSD experience, watching the sun set, gazing over the water of the harbour, and then walking through the park, looking at rainbows... Indeed a very nice way to end a session.