Japanese workers, especially the salary man, are characterized by spend many hours a day to their works, so it is normal looking for some kind of energetic or vitamin supplement to help them take the necessary forces their jobs required. Of course also students or athletes consume it to try to improve their performance.
In stores where drinks are sold, especially convenience stores and supermarkets, is normal to find a shelf devoted specifically to these beverages and are also present in the vending machines. That means in Japan should be consumed daily hundreds of thousands of these drinks.
There are many types and flavors, but usually are present in small bottles that facilitate that can be drink quickly. Perhaps usual consumption of these drinks is not the most beneficial for health. It is also possible that the effects are not really demonstrable or varies greatly depending on the person, but psychologically safe used to be encouraged.