I think each drug has its own little gift to us.
On top of that, I think that if you have the curiosity or urge to try or continue taking a particular drug then there is obviously some form of personal growth that you still need to get out of it. Its like the subconscious' way of trying to liberate something in itself to eventually give you a peace of mind. You would never take a substance that you know is not good for you unless there was some benefit you got from it.
e.g. MDMA has many great gifts. Teaching you how to just be yourself regardless of your company, being able to talk about next to anything to someone you trust (psychological therapy), some escapism and bliss which gives you a little helping hand along the way if you haven't yet found happiness when sober, it clarifies your emotions on next to anything, the list goes on.
acid (and mind altering drugs) breaks all rules of thinking and perception so if you like mind altering experiences it can give you new insights, new experiences that would have been normal and mundane if you were sober, revelations. its like being reborn again every trip.
pot can be great to tone down your mind and channel it into one particular thought or just to relax you.
ketamine is great to get disconnected and give you an out of body perspective on yourself and your life.
the list goes on....they each have their own magic that can help you or break you in some aspects.
but generally i take drugs because i'm quite in touch with myself and i can quite carefully see the personal growth each drug experience gives me. once i don't have the motivation to take a particular drug then i know i won't get much from it and it will just be to "get bent". so for me drugs are tools for personal growth.