Definitely not new theory. Been around for ages and more a more detailed way to breakdown and analyze your opponent's range and how many combos of hands he can have. For example, if you have Ax and 3-bet villain pre-flop, and get 4-bet, combinatorically you reduce his combos of AA by 50% and AK by 25%, but don't reduce his combos of KK or QQ. We use it when ranging people, as well as when we're creating default ranges.
Is this essential? Or new theory?
Definitely not new theory. Been around for ages and more a more detailed way to breakdown and analyze your opponent's range and how many combos of hands he can have. For example, if you have Ax and 3-bet villain pre-flop, and get 4-bet, combinatorically you reduce his combos of AA by 50% and AK by 25%, but don't reduce his combos of KK or QQ. We use it when ranging people, as well as when we're creating default ranges.