I went to a Japanese restaurant and tea was served during the meals...
My guess is it probably helps with digestion, so after a meal might be a good idea. However, if you're trying to watch your weight and don't want to eat too much then you can drink tea to make you feel more full up before eating because it is mainly water so like it doesn't have too many calories or anything.
Also green tea is good for you, it has anti-oxidants and reduces stress, so I try to drink it every few days.
Also you're not supposed to have sugar with it, but I do because I don't like the taste that much otherwise!
