"Double locking" handcuffs is SOP and has nothing to do with profiling. There are a couple of reasons. Unless double locked, handcuff halves are connected by a ratchet mechanism. This means that either intentionally or unintentionally, the ratchet can be closed further than necessary, which is potentially harmful to the person in custody (and which is sometimes employed by the person in custody in order to ground a complaint that "the cuffs are too tight"). Beyond that, unless double locked, the ratchet is susceptible of shimming, allowing an experienced person to escape the cuffs.
"Double locking" involves just pushing a pin or sliding a latch, which then moves a solid bar under the ratchet and preventing movement of the sliding side of the cuff in either direction. Double locking is routine and done whenever a person is cuffed.