While re-stringing and re-gripping your racquets on a regular basis is essential for optimal performance, most players these days would benefit from customization beyond the basics of just choosing a string, a tension and a grip. One of the reasons this is true is that racquets today tend to be way too light. It's true that a lighter racquet is easier to swing, but the trade-off is that when a lighter racquet connects with a ball that same lack of mass actually translates into less power and less stability.
The racquets I play with come from the factory weighing around 270 gms and they are balanced head-heavy. Take a look at the label below and you'll see that I add over an ounce of weight to my racquets, sufficient weight to leave them significantly head-light.