There is an increasing tendency for acne treatment regimes to include some form of moisturizer. The reason for this is quite simple: If your skin is dry, your body will start to produce more oil.
This is why, that no matter what topical treatment you are using, you should not ever over wash your face. Your skin will become irritated, and may eventually start pouring out oil at an insane rate. This is also why it is not good to wash your face right before you go to bed at 11pm and then again when you wake up at 5am! As a general rule (and this will vary per person), try to leave at least 10 hours between face washings. Even products with moisturizers may invoke a negative reaction from your skin if your skin keeps getting all of its oil stripped off by cleansers.
Remember: your body naturally maintains itself. When you get hot, your body sweats to cool you down, when you get cold, you body shakes to warm you up. When you get sick, your amazingly complex lymphatic system works around the clock to cure you. Cut yourself, your body jumps into action to clot the wound and start healing. This extends to even smaller items. Do a lot of hard work with your hands? Watch your skin get tougher as you develop calluses. Play guitar, and your finger tips will develop calluses as well. Well, no surprise here, if you keep drying your skin out with chemicals, your body works to produce more oil, to help keep your skin moisturized. This means that chemical treatments that just dry your skin out may work for a short period of time, but after awhile your body will adapt and start producing even more oil than normal, possibly making your Acne even worse.