I have a 9mm Sub-2000 that uses Glock mags.
I would imagine that the top two design requirements for the Kel-Tec Sub-2000 designers were:
1) Gun must be profitable - production cost must be less than probably $150 or so.
2) Gun must reliably shoot bullets.
I'm sure it had a bunch of others relating to folded size, max weight, color, mags it must accomadate, etc, but those will be the two primary ones.
The purpose you put it to will be up to you, just like any other gun. You can hunt with it, use it for home defense, stow it away as a boat gun, use it for target shooting, plinking, etc.
I'm sure that in the design requirements somewhere was one for it to be used by my granddaughter to load up a 33 round mag and knock down steel plates with it, since that's what it's primarily used for. But I have no doubt that it could just as easily fulfill any other role you desire it to.