Controversial. Bee venom therapy (apitherapy) has been used as an alternative treatment for multiple sclerosis and cases of chronic pain. I have never done it myself but have read about it. At this point i cannot recommend it due to insufficient studies demonstrating a beneficial effect.
Insect allergy. Some people develop severe allergic reactions after a bee sting...An allergist tests them and then makes a specific vaccine to give them. Over time they develop resistance and won't have a bad reaction if stung again.
Many conditions. The most common treatment using bee venom is for desensitization of an individual who is allergic to bee stings.
Some therapists use bee stings as a treatment for condition similar to arthritis, but this is controversial.