The stock cables are sufficient, but there's room for improvement....just like a lot of parts on these trucks! A good analogy is the intake, the stock intake flows sufficiently well for a stock truck, and even modded trucks (heck the 6.2 makes 400+ hp at the crank thru it). And you don't hear of guys having problems or issues with the stock intake, but many still upgrade because it's a slight improvement and increases the size of that big straw the engine is breathing through. Stock is sufficient, but aftermarket alternatives provide additional benefit.
Similar with the cables. Stock is sufficient, but increased cable gauge increases the size of that straw the main power system is drawn through, which reduces voltage drop.
My 00 F-150 has 4awg battery & alternator cables and that truck has 2 power windows, locks, ac, and a 6 disc cd player with 4 speakers. My 12 Raptor has the exact same 4awg battery & alternator cables and it has all those same creature comforts drawing electrical power, PLUS 3 more power windows, 6 more speakers, factory sub/amp, heated & cooled seats, huge nav screen, factory electric fans, cameras, way more controlling gadgets, etc. Then upfitter switches to add even more power drawing items in. My Raptor has a larger battery and a larger alternator than my 15 year old f150 to power all that stuff, but the same 4awg power cables.
And just because Ford designed it that way, doesn't mean it's the most ideal. It's a balance of cost, performance, reliability, etc. 4 AWG cables are still sufficient so it doesn't hinder performance and keeps costs down (less copper), plus they share many parts, harnesses,etc. between models, I'm sure every f150 uses 4AWG whether it's an XL with manual everything, or a Platinum with power everything. So 4 AWG from the factory is a good middle ground, WAY overkill for a manual-everything truck, and sufficient for a fully loaded electrical glut. This mod for an XL/XLT, not even worth it. This mod for a Raptor that's factory loaded with electronics, and many aftermarket mods adding even more, definitely a good one to do IMO.
It's not going to bump your 12v system to 16v, just like an intake isn't going to add 50 hp. But typically in most vehicles it's worth a couple tenths of a volt....just like an intake is usually worth about 5hp to the wheels lol. But every bit helps.
The other benefit with this kit, more of a long term thing, but the copper is fully enclosed and sealed. The cable lugs are enclosed ends, and tinned, and the connections are hydraulically crimped then shrink wrapped. No exposed copper to oxidize with the tinned lugs, and no exposed copper stranding to oxidize and cause problems. A problem with many vehicles once they get old is battery cables corrode from the copper being exposed. When it's sealed up, they stay reliable for a lot longer. The OEM cables are open crimps, copper strands exposed. It's rarely a problem within the first 5 even 10 years, but long term, it begins to peek it's ugly gremlin head out. Since these trucks are still in that 5 year range, battery cable corrosion issues are still pretty much unheard of, but another 5-10 years, they'll start popping up as they get up there in age.
This pic isn't mine, but it shows a clear example of an older cable with exposed copper from the open crimp, with the copper oxidizing, which increases resistance, and causes a poor connection and higher losses. You won't get that with fully sealed and enclosed cables like the kit from Jokerz
So recap....stock is sufficient, but this kit is an upgrade stock to even better as 1/0 will have lower losses, which means less voltage drop, stronger voltage to your accessories and OEM systems even as you add more and more items, and better construction for improved reliability over stock.
Price may seem expensive if you just look at it as a few pieces of wire, but if you dig into it to price it out yourself to the same level of detail, you'll quickly see it's a fair price. The fuse setup is almost $50 in itself as it's not a cheap amp kit fuse that will melt down. The tinned copper lugs are $1.50-$2 a pop. 1/0 high strand count super-flex cable runs anywhere from $2-3 a foot. Then add in tech flex, moisture/chemical resistant shrink tubing, you're well over $100 in materials, and don't have anything assembled, nor directions, nor the tooling. These are pre-made, hydraulic crimped, exact-fit to the Raptor, not a universal kit, and come with color directions with step by step exactly how it installs as many folks aren't too comfortable with messing with electrical.
Sorry for the long reply....I'm an EE so I get pretty geeky with electrical mods on my vehicles lol.
I'm all for tech discussions, questions, & sharing info and opinions. I don't pass of the **** in the punch bowl as a tootsie roll though, I call it right out LOL. 
