It is known by each guy. When the girl will drink, she in part loses the control of the actions. Moral frameworks of any person are reduced. The person becomes not shy, showing the present feelings, there is no time sitting deeply inside.
Strongly drunk the girl it is not necessary. Otherwise it already can be regarded as a crime. I advise to drink only slightly. It is better to do it in domestic conditions, instead of at restaurant or a bar.
If, fairly I do not think it a way the best. It not fair! It can be the best together with other methods. This way will help only a few doubting girls to make the firm decision.
And then still the girl can be completely teetotal. Therefore despite of popularity of this method at men risk to name his worst. I give it mark 9 from 10 only for its super-popularity!