On Cars KPI works a little different. In terms of karts it's more of a balancing act and provides some stability, and gives wheel feel. But, it balances Camber gain and scrub radius.
It's a bit complicated to explain the way it works in Karts. But, it has a lot to do with caster, scrub radius, camber gain, and balancing front bite. It's one of the reasons karts balance right on the edge of the RF tire and if things aren't correct will obliterate the inside edge of the tire. This is part of the scrub radius deal, but it's a bit more
Older karts (Late 90's early 2000's) ran a range of 5-8 caster depending on the brand, which was built into the chassis. Then they started going up from there and made it adjustable with L blocks/heim joints. Where today 8-13 degree caster is common in higher HP situations. This helps adjust bite in the front end. Higher caster was needed to help transfer weight on the newer stiffer designs. Which is what you were originally asking about.
Now, couple that with higher cambers, and KPI creeps in. Because, KPI helps offset camber gain from high caster. Imagine it makes the arc produced less dramatic. It's sort of a package deal, stiffer chassis tend to run higher Caster, higher KPI. Camber remains roughly the same as older karts, but again with the higher caster this increased camber gain dramatically. So KPI helps to keep things in check. Since Camber gain is progressive, the different KPI give tuning options.
Shaw beat me to it, but, yeah that thread has everything in it I think. I haven't read it in a while.