Writing practice benefits candidates in the essay paper of UPSC by improving their ability to articulate ideas clearly and coherently. Regular writing helps in organizing thoughts and developing a structured approach to tackling complex topics. It also enhances critical thinking and the ability to argue effectively, which are crucial for scoring well in essays. Practice can familiarize candidates with managing time effectively during the exam, allowing them to complete essays without unnecessary stress. Moreover, feedback from mentors or peers on written work can further refine writing skills and boost confidence.