Kapalabhati means shining skull. One hypothesis is that it is cleansing for the frontal part of the brain. It is actually a Kriya rather than a pranayama and a prerequisite for Bhastrika.
It is a fundamental Hatha Yoga technique. Many benefits especially respiratory health, clearing mucus and activating of energy.
Contraindication, do not do this pranayama if you are pregnant or on your menstrual cycle.