The difference between a Principal Representative and a regular Representative with a voting weight of < 0.1% is that the votes of the Principal Representative are re-broadcasted by other nodes, and the votes of the regular Representatives are only communicated directly by the regular Representative.
What this means is that, if we had a network where every node holds less than 0.1% of the voting weight, then the practical difference is that a given node would need have direct communication with each voting node to collect their vote until they have enough votes to exceed the threshold - so we can't take advantage of the shortcut of re-broadcasting.
Is my understanding correct? Or is there something more to the distinction between the types?