There are numerous usage of Reiki, which one can only experiance by either going through a Reiki healing session or by undergoing the attunement process. But some of them are listed below:

Using Reiki one can practically cure all physical diseases.
Reiki can be used to cure all mental/emotional problems.
Reiki can be used to maintain/improve relationships.
Reiki can be used for improving memory/concentration.
Reiki can help solve career problems.
Reiki can even heal problems created by old karmic debts.
Reiki can be used to bring abundence in life.
Reiki can be used for achieving goals.
Reiki can be used to change bad habits.
Reiki can be used to balance body weight.
Reiki can be used for spiritual upliftment/meditation.
Reiki can be used to recover health, happiness and prosperity.
Reiki can be used to give healing to plants and pets.
Reiki can be used to give healing to future events and tilt them in your favour.

SOME OF THE DISEASES THAT CAN BE CURED:
Addictions, Allergies, Anaemia, Arthritis, Backpain, Blood pressure, Breathing problems, Cancer, Cholesterol, Diarrhoea, Dysentery, Fat, Headache, Heart problems, Stroke, Indigestion, Jaundice, Kidney problems, Phenmonia, Thyroid, Urinal Diseases, Insomania.

USEFUL FOR:
Housewives - Weight loss, hair loss, mental relaxation, family and children's problems.
Students and Teenagers - Increasing memory, career problems, acne, relationships.
Elders - Joint pains, diabetes, blood pressure, heart problems.
Professionals - Businessmen, C.A., Teachers, Engineers, Doctors etc.
Releasing tensions, achieving goals, increasing performance etc.

OTHER USES:
Spiritual Upliftment, Meditations, Will Power, Pleasure, Patience, Well being.