What a good one actually changes
Three things, mostly. They know processes your family has not been through, which matters enormously for anything non-standard — auditions, portfolios, athletic recruitment, service academies, direct-entry programmes. They provide a deadline structure that does not come from a parent, which is the difference between a task getting done and a task becoming an argument. And they read a student's list honestly, which is hard for a parent to do about their own child.
None of that is magic and none of it is secret. It is experience, time, and a position outside the family. Those are real things to buy.