The term "hypnotism" is more often used by "hypnotists" who use it for shows and acts of musing display.

Hypnosis is a form of therapy that those trained as hypnotherapists us to aid in therapy... some dentists also use it instead of chemical numbing.

It works, if you want it to. It's all up to you. Everyone has been hypnotised at some point in their life. (While driving is most common, or while listening to a favorite song on the radio and doing something else.. you soon realize OH, I was so caught up in... I didn't realize.)

It's very useful for meditation, relaxation at the very least.