I don't have much experience with the younger age groups, but I've found that with ages 14-18, too much training without a game tends to burn them out a bit. Regularly-spaced games give relevance to what they're doing in training; they can quickly see how what they're doing in practice relates to their performance in a match. As I have yet to see a player complete ten juggles without the ball touching the ground in an actual match, I'm not sure if that's the best measuring stick to determine how well the players are preparing for competition.
