8 x 8 or 6x6 was used to train for seeing open space and to teach sharp passing on a constrained field and tiny nets. Stressing movement, rapid passing simple touch pass, touch pass shoot score etc. No way either 8vs 8 or 6vs6 would be confused with playing a game. Even 8vs8 is used to learn space exploitation and rapid passing and movement. Most do not even have a keeper. In any case one can get a bit too intense, every youngster needs both mental and physical respite to progress. Th idea is to keep it fun and teach at the same time.