One of the most important things in tennis that will allow you to win more matches is depth on your ground strokes. Tennis is a game of taking advantage of openings and a huge opening indicator is the infamous short ball that lands on the service land. Once such a shot is noticed and taken advantage of, you are in a disadvantage. You gave your opponent the opportunity to change the momentum of the point and put it in his favor. You are now on the run and defense.
Hitting all your shorts with as much depth as consistently possible is what separates the great from the good. With depth, you give your opponent less room to attack, keeping the rally neutral until someone finally falls their ball short or goes for an aggressive shot from behind the baseline.
If you think about it, watch the matches that Rafael Nadal loses and wins against Djokovic. Whenever Nadal loses to Djokovic, he is usually outplayed in the depth game. The matches that Djokovic wins are those he was able to consistently put depth into his shots compared to Nadal. And when Nadal is getting his depth on his shots, he is an almost unstoppable force with the topspin he generates off his forehand.
Usually, the matches that Nadal loses are when he is unable to keep proper depth on his shots.