I don't know what the answer is but the can of worms has been opened. I wondered the same thing myself when I was looking at a 30th too. I don't think they are absolutely necessary. I believe the purpose was to add a bit more lift to the back of the boat when underway. This reason never made much sense to me as I thought the issue was a somewhat ineffective rudder at some rare and goofy situations. I believe it was officially called chine lock.
1996 Prostar 205 LT-1