It all depends how serious you are about training. If you are training for fun, and general fitness, then a few drinks is no big deal. If you want to be an athlete, or have an exceptional body, then the less booze the better.
Alcohol does not break down muscle mass, but it does inhibit protein synthesis, so that your muscles will have a very difficult time growing. It promotes the storage of abdominal fat (beer belly). It interferes with deep sleep cycles for up to 48 hours, in some cases preventing the release of growth hormone. It toxifies and over works your liver and kidneys, which play an important role in hormonal balance, specifically in a fitness perspective, your testosterone / estrogen ratio.