Lucas said pretty much everything I was going to say. If we're talking about hallucinogens, what they do is give you a vastly different mental perspective. This can be very valuable if you approach the experience consciously. Of course, this perspective shift is temporary, so you have to apply what you learn to the rest of your life, otherwise there is no lasting value.
In every discussion about drugs it should be noted that there are many different types of drugs and they all do different things and entail different health risks. Never do a drug without researching it first.
Erowid has loads of objective information about drugs.