The PCC is a niche gun. Many guns are niche guns, meaning they have a specific use that they excel. Any gun can be pressed for home defense say...a 1903 Springfield. It's a good platform, most will agree though that an old 03's niche is not home defense.
The basic shotgun's niche is upland and wing shooting, but another niche of the shotgun is its ambiguity and ability to do almost anything. It may not excel but it's very capable at many, many things. In other words, a shotgun is jack of all trades and does many well.
A 22 rifle's niche is small game and target shooting. Can it be pressed for big game? Sure, but it's not ideal. Can it be pressed for home defense, Sure but...?
A 22 is touted as one of the best all-around but really it has too much range, the round has too much penetration (in the home) and is too ineffective. A 22 rifle can be a jack of all trades but unlike a shot gun it does few well.
What's the niche of the black and the orange rifles (ARs and AKs) with their intermediate cartridges? They are not a great big game hunting rifle like a full-size service rifle. Are they really that good for home defense? What about penetration? What about range?
The black and the orange excel at medium game or varmints where decent range is needed. They excel at multiple targets like herds of hogs or groups of coyotes or feral dogs. These guns excel for target and sport shooting. Lastly though, their real niche is opposing others with black or orange rifles at real battle ranges.
What's the niche of a pistol caliber carbine?
In my opinion the following are the best uses for the PCC.
1. Property defense/livestock defense. It has the range but not too much range, the accuracy if properly sighted and the knock down power to put stuff down.
After killing a couple of your goats or calves, maybe killing or maiming your own dog in your fence, Fluffy and Speedy may make it home full of .22LRs or shot. You don't want Fluffy and Speedy to make it home.
I'm not an advocate of this unless it's the last resort. Something that comes on to your property and kills your animals and pets maybe even on your porch is a dangerous threat. Use restraint and judgement. A phone call to Fluffy and Speedys owners may be the best course. Then again, any animal bold enough to kill your cat or your dog in front of your front door may do the same to your toddler child or grandchild. This is why the gun needs to be quicky assessable, to stop the act.
A shotgun with slugs, a full-size service rifle and even an intermediate black/orange rifle may be too much for this type of duty.
This is the traditional role of a PCC. Think Winchester 1866/1873/1892 in those old pistol calibers...44 Henry Flat, 25-20, 32-20, 44-40...All are great property defense rounds out of a carbine.
2. As a quick sub-gun for home defense. With the detachable magazine (high-capacity Glock) the Ruger PCC can be loaded quickly and has much more controllable fire power than a pistol of the same caliber. (Yeah, I know this is debatable) ... It does not have excessive penetration like a service or intermediate rifle. It's quicker to load and get into battery than a completely unloaded pump or auto shot gun.
The thing is...
It has to be accessible for quick load and quick use.