being high at the gym seems to motivate you but fools you into thinking you are going to failure.. you tend to think you are going really hard but in reality you are more in tune with your effort when you are straight.
being angry also robs you of good performance..all that emotion, negative emotion, has a similar effect. time and time again, over years of training, the worst workouts were when things were bothering me.
the best ones were when i was at peace, and straight. without a doubt. and from what i read, that lines up with all kinds of well being studies.