When dealing with hypnosis you can either approach it by doing it alone or with a professional. If your basic goals are in the direction of personal development then self hypnosis may be an avenue that you should consider.
Sometimes self hypnosis can be more difficult and normally takes longer if you have not gained mastery over the proper techniques. This is where an advantage of a professional hypnotherapist can seem compelling; however working alone can be the best option in the long run.
One reason for this is that you can become more relaxed and trusting if you work alone as opposed to work with someone else. You can also hypnotize yourself any time of day or week, whenever you have the time. This also saves money in the long run as well, especially if you have several goals that you need to achieve, since using a professional can add up the expenses quickly.
If you are choosing hypnosis as a form of therapy, then using a professional is normally advised because it limits the risks and loss of control that can happen during a standard session. Depending on the problem, therapy is usually best addressed by professionals anyways.
Another reason that a professional is warranted is that repressed memories can arise. Granted, this can happen naturally, however a professional can be a great advantage when dealing with these issues. However, you should be wary of professionals who are eager to resurface these memories, because sometimes the subconscious mind can create memories of events that never happened solely because the hypnotist suggested it. By doing this yourself, you can assure that this will not happen.
You can actually much less likely to have repressed memories surface in self-hypnosis if your focus is on personal development goals instead of dealing with memories buried in your subconscious.
Self hypnosis can be done as often as you want which makes it easier to reinforce your goals which can make your success more likely to last. This can easily outweigh the benefits of using a professional who will get you faster results, but sometimes not long lasting results.