Maybe I should give a full example.
The weighting for one of my courses was
10% CP (Maxmimisable)
40% Mid Sem
60% Final Exam
As you can see it adds upto 110% instead of 100%. Assuming in both scenario you get 30/40 for mid sem.
Scenario 1, 7/10 for CP and 48/60 for Finals.
Your final mark = CP (0/0) + Mid Sem (30/40) + Finals (48/60)
= 78/100.
CP is not counted as it will change your final mark to 77/100 which is less than not having cp counted.
Scenario 2, 7/10 for CP and 36/60 for Finals.
Your final mark = CP (7/10) + Mid Sem (30/40) + Finals (30/50)
= 67/100
In this scenario CP is counted because if you don't count your cp, your final mark from mid sem and finals is only 66/100.