Are there any pragmatic uses of hallucinogens? Hallucinogens (psilocybin, LSD and others) are often regarded as risky substances, therefore they are banned in most places. 

Are there ways of using these substances that can be beneficial?
Or in other words can a hallucination, or a set of hallucinations, have a positive value?
Hallucinogens play an important psycho-social role in many societies. Their positive impact seem to be primarily religious (see Tripping the Way to God: Hallucinogens and Religion).
However they do play an important role in the lab inducing a state similar to psychosis. They also play a limited role in psychiatry.
Psychedelic psychotherapy as the name suggested is the combination of hallucinogens with a form of psychotherapy. It is not widely practiced.
Research into cannabidiol], a cannabis constituent with anti-psychotic properties instead of the typical high anxiety and psychosis symptoms, has been published; see  &quot;Cannabidiol, a Cannabis sativa constituent, as an antipsychotic drug&quot; by Zuardi et al, 2006.
Eli Lilly tried to make a drug based on these glutamate receptors interactions called LY2140023. It was shown to be ineffective by itself.
Many hallucinogens are used for alternative primary purpose like benadryl and nitrous oxide (laughing gas).