It is primarily function, as the others have mentioned. Also, keep in mind that khukuris are made in a region where Buddhist and Hindu beliefs intermingle. The handle, like the blade, has a lot of religious connotation which meaning has been lost over a hundreds of years. The rings in the middle of the handle keep your hand from sliding onto the blade, but they also have a "meaning" which is supposedly forgotten. The same thing can be said about the "cho" or that little notch in the blade between the bolster and blade edge. The flared buttcap does keep the khuk from shooting from your hand on the back swing, but the peened keeper where the tip of the tang is exposed is sometimes referred to as "the eye of God" since it sort of looks like an eye.