The side table only gets a slot for an object when the object is retained (has its reference count incremented) after creation. (Every object starts with a count of 1 at creation.) Before ARC, you could certainly have lots of objects that were never retained after creation. Since ARC tends to be more careful than a human about retaining objects (meaning it retains objects in more places), I don't know how much more load ARC puts on the side table, but I suspect it's not zero.