Alcohol is a big source of empty calories. In other words, all of these calories contribute to weight gain and can not be used to satisfied hunger or give you energy. In addition, the bigger problem is that alcohol makes us "munchy" - causing us to crave snacks and a lot of times it is the worst snacks that we reach for.
With that said, one or two drinks per day is absolutely fine. However, you will want to stick to hard liquor instead of beer and choose soda or club water instead of juice for cocktails. Wine is also a great choice if you stick to dry ones without sugar.