Like most substances, THC effect will highly depend on the quality of it, the way it's used (state of mind, environment, quantity, frequency,...) and the specificities of the user.
Like other new substances (or new actions) it can provide a catharsis effect. It's even more true with THC because of its psycotropic properties. It can help getting conscious of some habits / belief (the risk however is to replace old habits by new ones). Don Juan describes well why he pushed Carlito to smoke his special substances (peyotl + some other plants).