Take applying for a university as an example: the school hopes to apply for students who are not only studying, after all, there are many people who can study. What they want is an applicant with experience in getting along with others. Volunteer service represents a person's love, patience, and time and energy outside of reading; It also reflects that person's concern for society.
Besides volunteering, they also like people who have internship experience or start a club. This means that they have the ability to organize and get along with others.