As the serving team, we want to get up to the kitchen (No-Volley Zone) line. That is how we neutralize the advantage of the return team and hopefully score a point. Most of us were taught to get up there at all costs. This approach, however, can result in exposing your team to unnecessary attack. If you or your partner hit a high (or otherwise attackable) third shot, moving forward makes it easier for your opponent to hit a put-away shot. Moving forward before your partner also creates gaps in your line.
Bottom line: Before you rush forward, wait and see how your partner hits his/her shot. Then you can either move forward or stay back, in either case giving yourself the best chance to win the point.