It's said to increase your metabolism, so helps you lose weight. For this, some say you need at least 3 cups per day, others say 5 cups. That's a lot of green tea! Still others recommend taking it concentrated in tablet form to get results. Medical research has shown that green tea extract does increase your rate of burning fat.
Green tea contains flavenoids/polyphenols and white tea even more. It's supposed to boost your immune system and make you less likely to get heart disease, cancer and a whole list of other things. It's also said to be anti-bacterial.
Despite containing small amounts of caffeine, tea in general is said to be relaxing because of a chemical called L-theanine which induces a state of alert relaxation.