Cooperating might make it harder to fight your battles via the legal system. "Sure officer, come into my house/car and look around, gather or plant whatever evidence you feel is appropriate."

Even going down to the police station voluntarily for a "friendly" talk might screw you. In Salinas v. United States a man cooperated by going to the station. He answered some questions but was silent when officers asked if his shotgun would match shells from a crime scene. His silence was then used as evidence of his guilt and the Supreme Court decided that's OK.

You need to know your rights and explicitly assert your rights. The legal system is not going to do that work for you.