That is a very good question, I believe it is detrimental due to the circumstances, so I'll explain more.
Son graduated from high school he lived with dad. Only minor left is daughter lives with mom. Dad's child support doubles June 1 and dad remarries shortly after, typical child support and triangle to remove old wife from picture for the new wife. Dad has daughter for summer and convinces her she wants to live with his new family, starts court battle. Daughter returns to mom and after getting away from the manipulation decides she isn't sure where she wants to live, doesn't want to choose, hates being put into the middle of this fight and just wants it over. Court battle is still ongoing.
Son goes into armed forces. Dad asks mom to postpone court date for son's basic graduation, mom refuses. Dad refuses to give mom any information about him, saying she needs to talk to son who is in basic. Dad knows son is unreachable with very limited communication ability and information sent to him is to be shared, won't even give her an address. It's obvious Dad is withholding this info to prevent mom being able to go to Son's graduation, and if he can't prevent it he's setting up a hostile environment of his new family against her at this event.
Dad plans to take daughter thursday night for the birthday visitation and keep her Friday to attend Son's graduation with his new wife and her son, excluding mom in this arrangement. Mom offers proposal to take daughter to graduation with her and spend a little time with son after ceremony, leaving right after lunch and invites Dad to join them trying to create an amicable environment for all for the few hours before she lets Dad have his time with both children.
So the question is, is it detrimental to daughter (and son) to let Dad make his daughter a part of his scheme to exclude and make Mom an outsider at this family event? How much trouble can Mom get into to refuse to let Dad have daughter Thursday knowing she will not be returned at the court ordered 9am Friday?
This would be an isolated event. Throughout this court battle mom has played by the rules, gave dad an extra weekend in Sept, offered an extra weekend in Oct that was turned down, gave time on her weekend so dad could take daughter out after a school performance he attended, etc. Dad has been hostile, argumentative, took away almost 3 weeks of mom's summer time and refused twice to let mom have daughter when he was traveling for work during those 3 weeks, basically he must not have heard any advice from his lawyer to make himself look good for court.