Obviously, officers can ignore the statutory directive in 15A-501 and make an immediate unarrest where that is appropriate. This satisfies the intent of the statute and also allows for immediate release. Custody triggers the need to prove probable cause at the time custody begins. That may be difficult in some investigations. You do not need probable cause to conduct a noncustodial interview.
Voluntariness rules are more relaxed if the suspect is free to leave.
A suspect will have difficulty proving improper threats or promises coerced a confession if the suspect could leave at any time. You can ignore language that otherwise might be an invocation of right to a lawyer, which cuts off police-initiated interviews. This language should be used by all officers who wish to conduct a noncustodial interview. If you provided transportation to the place of the interview, offer to provide transportation back to the suspect's residence. If you conduct an interview at the suspect's house, offer to leave upon request.