[Koko Ed]

The only negatives that come from practicing is the toll on schoolwork (the mentors could regulate that and make sure they keep up on their schoolwork. It's no different than applying academic standards to athletes. You want to play? You do your work or you sit. Simple as that. FIRST should never come before school and anyone who thinks otherwise is irresponsible and should not be mentoring the kids) and that practice is not a real live match with variables and barriers to challenge the driver's skill.
Other wise there really is no negative to practicing with the robot.