It is a lot of atomic +1 and -1, meaning possible thread contention, meaning that no matter how many cores your hardware has you have a worst case scenario wher

It is a lot of atomic +1 and -1, meaning possible thread contention, meaning that no matter how many cores your hardware has you have a worst case scenario where all your atomic reference counted objects have to be serialized, slowing everything down. I do not know how ObjectiveC/Swift deals with this normally, but making that operation as fast as possible on the hardware can have huge implications in real life, as evidenced by the new Macs.