Training is such a powerful tool, and so it's dieting. Those two combined can maximize your physical and mental performances, depending what your end goal is. When you train to develop a skill, run a marathon or perform a dance routine, your diet must follow your goal (Performance) so that your body can have the right type AND amount of nutrients to sustain your training. As a general rule, the more hours of strenuous training, the more (clean) calories will be needed.
If you train to lose weight, compete or be a fitness model, you'll have to work hard with both your diet AND training. Your goal in this case is Look, your body appearance is what you focus on. You'll need to be very strict with your diet, and at times your training will suffer from the lack of calories. But you'll get used to it and your energy will adjust.
During the years I was competing, I was pretty lean year around and didn't allow myself to gain weight (nor strength, consequentially), my goal was LEANNESS, rather than being stronger or able to perform different skills. I used training to complement diet. Diet alone would have left me skinny and flat. Lots of cardio and weight training gave me a shredded look and this combination worked well for few years. Only thing, it didn't leave much space for improvement or gaining new skills, my energy was limited and I knew I had to use it wisely.
The moment I put Performance before Look, I started to explore my body in a whole different way. I added pole dance back to my routine, more stretching and few weeks ago I even started contorsionism. I learned new skills, added muscle mass and strength. I faced body challenges I wouldn't have even considered in the past, because I was all about the "Look".
You can have times where one goal prevail on the other one and vice versa. I still spend a lot of time taking care of how I look, after years of doing that I wouldn't have just stopped :) Clean eating is a good habit and knowing your body makes things easier (knowing how much you can eat of something etc.).
To sum it up: Performance needs quality diet and training. Look needs strict diet and training.
See you next post!