What opinions are there for taking a gap year or other measures before going to grad school?
Graduate school requires a large investment of time, personal energy, and financial resources. Graduate school also represents a commitment to a particular career direction, and, by definition, a winnowing down of certain options. (For example, if you choose to go to law school, it is less likely that you will become a doctor – although not impossible!)
Taking time off before attending graduate or professional school is an excellent idea. A break after finishing your undergraduate studies affords you some time and perspective to confirm for yourself whether you remain committed to your career choice. Time off affords you an opportunity to further develop skills and habits that will make you more successful in graduate school. (When I went to law school, some of the most successful students were those who had already developed disciplined work habits that they translated to study skills.)
Finally, after you finish graduate school, especially a professional school like law, business, or medicine, you likely will want to start right away on your career path. Time off after you finish graduate school will impose some opportunity costs. Therefore, taking time off after college is probably the best time in your life to take time to explore our big and beautiful world.