>>347275871. THC can speed up metabolism, which is why you can have massive munchies without getting fat as fast as you usually would.
2. Personally, I use it to recover. If I've had a really fucking amazing workout I just have a special brownie that evening, it relaxes me so much and makes me sleep much better.
3. Smoking it can, since it will fuck up your lungs. Eating it/drinking it definitely won't affect your muscle gains in a negative way.
Though in the end, weed CAN make you lazy if you don't use it right. If you use it as a tool, it will most definitely enhance your life, but if you make being high the end goal of your life, then yeah, your gains will start to suffer from your laziness and lack of motivation.