The iPhone 5S is set to be revealed in two weeks, and being an S-type update, this typically means that Apple has spent time optimizing and maximizing under-the-hood performance of the iPhone that preceded it, in this case, the iPhone 5. The rumor mill says that the next iPhone will sport an A7 processor that is 64-bit and 31% faster than the A6 found in the iPhone 5. What would 64-bit processing do for the iPhone? Well, iOS 7 is intense on things like transparency and other graphical elements, and an optimized 64-bit processor could make those as smooth as butter. That's the benefit of Apple making its own mobile processors:
One of the biggest—if not the biggest—advantages Apple has in not being reliant on merchant silicon (they don’t buy standard application processors designed by others) is that they can customize the A7/A8 etc to exactly fit their own apps / services frameworks, without making generic design compromises.
To see this best, contrast Qualcomm, whose processors will fit in hundreds or thousands of different Android models to Apple, whose A7 will go in to the iPhone, iPad and possibly the iPod and iTV. Because Qualcomm must support so many potential vendor configurations, they are forced to design by the 80/20 rule. Meanwhile, Apple can strip out absolutely everything it doesn’t want on-chip, and add specific things it does, such as DSP or graphics capabilities which iOS is designed to use.
Of course, just because Apple is testing these processors, that doesn't mean that they'll see the light of day in the iPhone 5S. Other rumblings say that the next iPhone will also contain a fingerprint sensor, motion tracking sensor, a camera that supports a 120 FPS slow-motion mode, a gold color option, and possible even a 128GB option as well.