Memory lane: before the birth year rule, I remember a situation where my daughter (dob 09/04) who was rostered on the 03/04 team guest played with our 04/05 team for a 8v8 game. They must have been 10 or 11 at the time. The game ended and the field was being prepped the for next game, and 11v11 game by our 02/03 team. As the youngers girls were walking off the field, they turned and asked my daughter if she was coming and she said no, I'm playing GK for the 02/03 team. I will never forget the look the youngers girls gave, the sheer size difference (pre-puberty vs. post-puberty) was very noticeable.
My daughter has always played up but I agree...it shouldn't be done if there is a risk factor involved or if the player is not making an impact with that team.