A handgun round in a carbine barrel typically gets a boost in velocity & terminal energy.
It also increases the practical shooting range of the caliber beyond a handgun (greater likelihood of a hit farther out).
It also makes a good companion to a handgun in the same caliber.
For situations where a 7mm Mag is not needed, it can offer good range without overkill.
I have 16-inch carbines in .357 & .44 Mag.
Both are 100-yard guns (more, if I wanted to push) perfectly suitable for deer, hogs, bear defense, and so on.
Both are very handy to carry, lighter than full-length rifles.
The concept appears quite understandable to me.
Denis