All weapons are situational. Until fairly recently, my only rifle was .22LR, but I had 9mm handguns, so a 9mm carbine made sense. For outdoor/SHTF home defense purposes, the longest shot I would be able to make without shooting my neighbors' homes is 50 yards, which is quite feasible with a carbine but not something I'd care to attempt with a handgun. Beyond that, I would definitely switch to .223, but at that point, I'd be standing in the street and an easy target myself. Bugging out is another story, but in an urban/suburban area, "long range" can mean anything beyond arm's reach.
All things considered, a PCC isn't a must-have gun, but if you can share ammo (or better yet, mags) between a handgun and a carbine, what's the downside? You will lack the range and velocity of a true rifle caliber, but I see no appreciable reason to doubt the capabilities of a quality handgun round combined with the increased range and accuracy of a carbine, however slight those increases might be.