Initially caffeine was thought to improve strength and stamina across the board and was used widely in the sporting world. At one point certain levels of caffeine was considered doping and subject to suspension. In 2004 this changed and it was no longer a banned substance. Caffeine is widely used in day-to-day life so it is hard to control. There is an enhancement effect but studies have shown that it is variable in its effect and significance.
Caffeine has been shown to improve performance at normal and slightly elevated intake levels and that taking further higher levels adds no further benefit and in fact, may actually decrease performance. Caffeine is particularly effective for certain sports that combine intermittent effort and endurance, such as soccer, rugby and hockey. But most of all it is important that the studies were done in elite athletes, who unlike most, are able to perform and train to exhaustion level. There is no solid evidence that there is a benefit for amateur athletes.
Athletes are competitive by nature. Looking for the competitive edge they think if a little is good than more is better. This is not the case; high doses of caffeine leads to loss of fine motor skills, decreased technique, sleep disturbance, high blood pressure and irregular or speedy heart rhythms that all can lead to decreased performance. Also the peak effect of caffeine is about an hour after it is consumed, loading up on energy drinks before the start of the game will not help.
Other studies have found that although very high doses of caffeine may lead to dehydration it is not the case with regular to high doses, especially when taken in drink form, as the fluid intake is greater than the loss.
The bottom line is that for recreational athletes, taking their regular caffeine an hour before your sport can be beneficial. An elite athlete may double or triple this amount, but usually in a controlled high performance environment to calculate the right amount for an individual. Any more than that does not help any further and may actually make things worse. Caffeine as a stimulant in sports, just like in life, can be enjoyed and used wisely and in moderation.