This type of training game is more often used to practice a certain structure that arises from a specific opening, and thus is a type of practice used more towards the higher levels of play (International Master+).

The thing is, if two amateurs are playing, neither of whom deeply know openings, then the starting position (or 4-5 moves in) is essentially new territory, like what might arise for a Grandmaster 15-30 moves into the game. Does this make sense?