We don't always have the time to play as much table tennis as we would like to. We get caught up with work, school, or some other activity that limits our ability to focus on our game. So during periods where training time is limited, what is the most critical aspect of the game to work on?
Sure we could practice our loop or our smash, but is that really a good idea? If you haven't been practicing, chances are your loop or smash won't even come into play because of the weakness of your serve and serve return. This limitation will enable your opponent to deal with your serve very easily and put you out of position early in the point. You'll end up having to make high level shots that require hours of practice just to stay in the point. In addition, you will not be able to effectively prevent your opponent from attacking off his/her own serve, which will lead to even more difficulty. So with a weak serve and return of serve, when will you be able to use the forehand loop you practiced?
This should make the point clear that when time is very limited, work on your serve and serve return. At the very least, you will not be at a major disadvantage early in the point and will have a better chance of staying in and perhaps even winning the point. If you neglect your serve and serve return, you will not be able to effectively enter into a rally and will always be at a major disadvantage and have to make very difficult shots in order to win.