Without asking each manufacturer it would be hard to say. But, some use them for checking Camber gain, Ackerman, and with the right tools it can be used to check Caster. But, again without measuring and knowing what angle the stops go to, you'd have to check and measure everything to ensure it's correct.
Fortunately for Karts it's much easier to use a digital level or angle finder and just measure the Caster block degree from 90 in relation to the front and back of the kart. In other forms of motor sports that use suspension or a different type of spindle and hub setup, caster has to be measured with the sweep method. It can be measured on the spindle in some instances, but this might not be as accurate depending on how they're made. But, none of this applies to a kart really, since we can measure right off the caster block. Or you can do the sweep method to ensure that the marks on the chassis are correct or find the angles of some older chassis that weren't marked or check to make sure something isn't bent.