Apple's announcement that the new iPhone 5s would sport the world's first, commercial 64-bit processor in a phone, the Apple A7, caused a ton of confusion that's still rippling through the internet. Somewhere between dismissal and deification lies the truth - does 64-bit really matter right now, and if so, for whom and how? Mike Ash adds to the answer:
Adding it all together, it's a pretty big win. My casual benchmarking indicates that basic object creation and destruction takes about 380ns on a 5S running in 32-bit mode, while it's only about 200ns when running in 64-bit mode. If any instance of the class has ever had a weak reference and an associated object set, the 32-bit time rises to about 480ns, while the 64-bit time remains around 200ns for any instances that were not themselves the target.
In short, the improvements to Apple's runtime make it so that object allocation in 64-bit mode costs only 40-50% of what it does in 32-bit mode. If your app creates and destroys a lot of objects, that's a big deal.
Yes, it's complicated. But that doesn't make it unimportant. If you want to know more, read the whole piece.