It depends how many steps of Comfort Zone are still left, and it depends how much CP you need for the next skill. Activation of CZ requires 66 CP (cost = +66). Full return is 80 CP (cost = -80). Net gain is 14 CP (cost = -14). When there are two steps of CZ left, you are still missing 2x(-8) returning CP, so net cost = +2... in other words, if you still have 2 steps of CZ left, you have spent 2 CP, with no gain yet. When you have only 1 CZ stack left, your net cost is -6, so you actually gained 6 CP. When you have no CP steps left, you would have gained the full 14 CP (cost = -14).