Not only in Prelims and Mains exam but even you will not be able to express or talk in front of the UPSC board during your Personality test. Reading newspapers and magazines will help in increasing knowledge of Current affairs. Moreover, Government exams are based on questions from Current affairs. They do have sections on current affairs ultimately checking on your General Knowledge. Students need to be in constant touch by reading newspapers and magazines since Current affairs are not static and change very frequently. This helps UPSC in the selection of a candidate who is abreast with what is happening in their own country and world.
It helps in your own analytical, logical and interpretation of latest happenings and issues like current social issues, election reforms, economic issues, international relation etc. Reading newspapers and magazines, using different websites as your resource will help you in understanding and gaining knowledge.