In short: I have found that this yields much better results for getting lean and building muscle than the most common method of eating less and training more (usually with the intention being fat loss and not muscle gain). I have found that I can get leaner and stronger eating more but simultaneously training harder. And when you eat more you CAN train harder, thus burning more calories. Ultimately weight gain and loss (be it from fat or muscle) is dependent on calories in vs. calories out, but there is also a hormonal role when it comes to these things. Calorie restriction will result in fat loss, but over time that becomes less and less as the hormones involved in fat storage become downregulated. When you eat to match your energy output, you maintain the hormonal equilibrium necessary to burn fat and get lean, while at the same time building muscle. In other words you are keeping your metabolism going vs. shutting it down with over-exercise and calorie restriction. I have found that, combined with this, intermittent fasting, where food intake is limited to a 4-8 hour period each day, also can play a key role in making lean gains. It seems like when people eat and train more for performance as opposed to aesthetics, things tend to work out a lot better for many people, as I am starting to find out myself.