need sugar during or after your workout. If you just drink water your body produces 100% cortisol, but if you have a drink with sugar your body only produces 6% cortisol. Cortisol contributes to fat/weight gain, so I guess it depends on your goals. But this is why chocolate milk is so popular as a post drink.

You need to eat a healthy carb during your lunch and a little during your dinner, don't worry healthy carbs will only help you gain lean muscle. Also add a fruit low on the glycemic scale (clementines are great) to each meal, this raises your metabolism. Eat about 150 g of protein throughout the day. And if you are really hardcore eat a healthy protein/carb snack in the middle of the night to keep feeding your muscles.

Personally I like a pre workout, because it gives me so much energy and I get a much better workout. However I'm pretty sure I'm contributing so some health consequence in my future (testicular cancer is one that studies have show when using these kind of workout supplements).

Bottom line, no you don't need to buy his stuff. Just get some quality protein, learn what a healthy carb is and workout hard so that you are sweating every workout. You'll shred like crazy if you follow all this.