The Optional is the only type of subject that aspirants get to choose in Civil Services Exam (CSE) and whose marks are considered in merit calculation. All the remaining papers are either the same for everyone or are only qualifying in nature
Optional subject exam is the key to success in the UPSC CSE. In GS Mains exam, you may not be able to make much of a difference but in Optional, you can even have a lead of 20-50 marks if the choice is good and the efforts have been put in the right direction.