My personal view:
They have a specialized niche where they are a fantastic choice.
When compared to other weapons, PCCs fall into an interesting little niche in my view.
They do not conceal or carry as easily as a pistol, but can make more reliable hits are further distances and some have higher capacity.
They do not hit as hard or at as long range as rifles, but are lighter and easier to conceal or carry.
Every weapon man has made has a specific purpose in mind. When used in that mode, it probably shines. When used outside of it, the weapon will normally lag behind other weapons specifically designed for that purpose. However, weapons can be adapted to better fill certain roles.
For example: A 28" shotgun with birdshot is an ideal weapon to hunt bird. (its original, specific purpose. I know not all shotguns were designed this way, but for this argument I'm referring to the most commonly owned pump guns, 870s and 500s.) It doesn't do as well in a home defense scenario. That being said, a shotgun with buckshot or slugs and an 18" barrel is a much more desirable HD weapon. Not its original purpose, but adapted well to fit it.
Pistol Caliber Carbines (or SMGs or Machine Pistols) were originally designed as short range suppression weapons designed to be used on full auto. Almost all military forces in the WW2 era used them for this purpose, to allow their bolt action or Garand equipped buddies the ability to maneuver, close with the enemy and destroy them. It was the house to house fighting towards the end of WW2 that really showed everyone involved how handy a man portable, intermediate cartridge automatic rifle would be handy in modern warfare, and thus the "assault weapons" were born.
So if we have rifles and pistols, what niche would a PCC fill (especially one that isn't capable of automatic fire...)?
I will preface that to me, the ideal PCC to fit this role should be a high capacity SBR, preferably with a folding or collapsing stock. (thus more compact than a rifle). Common examples would be an SBR'd Uzi, or SBR's Sterling, H&K MP5 style weapon, UMP, etc.
To me, it fits 2 roles better than either pistols or rifles.
1) Home Defense in a suburban setting (I'll take a rifle in the country)
2) An in car weapon (not trunk gun)
1)Home Defense:
Like many of you, I live in a brick home, with neighbors nearby no matter which direction I look outside. Penetration in the suburbs matters, and I'd rather not wind up with holes in my neighbors house if I have to use a weapon. Certainly frangible rifle ammunition helps if you're only option is a rifle, but a PCC would be far LESS likely to over-penetrate. Carries more rounds than a shotgun or pistol (generally), and is lighter/easier to handle than rifle.
Advantages over a handgun:
Larger capacity magazines
A 2 handed weapon with a stock is far easier to make accurate hits with than a handgun
Advantages over a rifle:
Less likelihood of over-penetration
Lighter, easier to maneuver in the home
Advantages over a shotgun:
Higher capacity
Lighter, easier to maneuver in the home
2) an in car weapon.
This is kind of a unique role, but one I think is worth considering. Holstered pistols are hard to draw while seated in a car. Rifles are long and cumbersome inside a vehicle. The PCC balances this out nicely. In a a problem arises type situation where you must be worried about mobs or carjacking, or even a simple hurricane evacuation where traffic is jammed and tempers are short, throwing a towel over a PCC allows you as a driver or passenger to defend yourself in car. The advantages over our other common weapons are basically the same in this situation, so I see no need to spell it all out again.
Anyway, for the Way Too Long, Didn't Read (WTL;DR) crowd:
A PCC has a valuable niche to fill in a civilian arsenal. While you can use other weapons for the scenarios I think it shines in, its hard to beat it in regards to those situations.
And if nothing else, there's something awfully cool about subguns.
I'd love to hear others thoughts on why I'm right or way off base.
