Almost never - and never without a lawyer. By the time investigators contact you, they already have documentary evidence. Their goal is to lock you into a statement they can use at trial. "Cooperation" in the casual sense - giving an interview, handing over your phone, signing a consent-to-search - does not get you a better deal. It gets you a worse case. True cooperation is a formal proffer with your lawyer present and written use-immunity from the prosecutor. That can sometimes reduce exposure in multi-defendant cases, but the decision has to be made with counsel who knows what the government already has. If an agent contacts you, say "I want a lawyer" and call Bank & Munns.
