Increase Muscle Mass and fat loss.
It's assumed that testosterone is a contributor to increasing muscle mass. These studies showed that an increase in testosterone levels in men led to less fat and more muscle even without exercise. Because of this, expect more men to take natural testosterone enhancers while working out to give them a competitive edge.
Boost sex drive
There are many studies out there that show low testosterone being one of the main things that effects a man's sex drive. Therefore, it's obvious that enhancing your testosterone naturally can lead to a higher sex drive.
Improvement in Self Confidence
The above points could possible lead to low self confidence on their own, but it's also proven that a lack of testosterone in men can also lead to a lack of self confidence. It's also proven that the more confident you are, the more testosterone you produce - kind of a manly chicken/egg theory.