Alcohol is Hashem’s gift to man. Not only does moderate drinking make one happy, it is also a miracle drug, good for the brain, the heart, and everything else. But the cup is מלכות, which contains within it a negative side, אף וזעם, that comes out when one drinks without control. One must use the power of the intellect, כח הבינה, to control not only the quantity of ones drink but also how one directs and utilizes the feelings that come from a moderate dose. Does one direct them to the right or to the left, to happiness or to anger. The negative side must be directed to the kelipos, and the positive side to serve Hashem with simcha.
(Based on the kavana that the Baal Hatanya wrote in his siddur to have when spilling the makkos on Pesach. Since he generally did not include kavanos, this one exception must be meant to be accessible to all.)