This steady, relentless pressure over the course of the game will harass and tire the opponent. It will cause the offense to make bad passes and force turnovers that opponents would never make if they were allowed to dribble up the floor uncontested.
For our full-court press, we may simply play full-court man-to-man "pressure defense". This is a good full-court defense for younger players to play because:
It is effective. Just a little man-to-man pressure will often cause the offense to turn the ball over. More experienced (high-school level) offensive players can break this defense down, but usually not middle-school players.
It is easy to teach and requires little practice time. A full-court zone press on the other hand requires considerable practice time to learn it correctly.