Do some CKD plans call for two carb-ups?
yes, like bodyopus and anabolic diet
If so, what are the advantages/disadvantages of them?
advantage is a higher anabolic effect (for most at least)
disadvantage is you'll probably overspill and gain fat (not for all)
What type of person benefits the most from each type?
there is no one type of person suited for either
Mr.X