I heard two people learning about Issur Kolel and Issur Moisif. They kept talking about the Rambam's Nekudah Niflaah. What is it?
The RAMBAM (Perush ha'Mishnayos to Kerisus 3:4) explains that when the Torah prohibits eating meat with milk, and benefiting from a mixture of meat and milk, it uses the same phrase, "Lo Tevashel." The use of the same word teaches that when the Isur of Achilah does not apply, the Isur of Hana'ah also does not apply. With regard to a mixture of Neveilah with milk, if the prohibition to eat meat and milk does not take effect because "Ein Isur Chal Al Isur" (since the mixture is already prohibited to be eaten because of the Isur of Neveilah), then the Isur of Hana'ah also does not take effect, and thus it cannot be an "Isur Mosif"! (The Rambam refers to this explanation as a "Nekudah Nifla'ah" -- a "wonderful point.")