Winning doubles is when both partners are working together, in tandem. Similar to ‘volleyball’ when players set up a team mate for a spike, the same philosophy when a team serves playing doubles.  When I serve I make sure I can hit the serve ‘wide’ on the deuce court and ‘wide’ on the ad court.  With my partner at net, they follow the angle of the serve and await usually a weaker return than normal, due to all the running the returner has to do and that they are now near the side fence and off the court. Though it may be returned, it becomes 2 players against one, the returner is still outside the court after they hit.  Too many players hit hard serves with little placement and at times the ball is returned as hard or harder.  It becomes much harder to hold serve and win points. So Placement vs Power when serving in doubles is the key to winning tennis.