When in high school, taking the SAT is a vital part of your experience. 

Due to recent changes, you no longer have to make an appointment to come and take the test. However, I think it is easier to make an appointment and it is more effective to make an appointment rather than just walking in. 

When you schedule an appointment you can be more aware of when that date is and it gives you time to prepare. The time it takes for someone to study and learn the full content could be longer to shorter time span based on the person. When you schedule an appointment you can pick a date that is helpful to when you are able to learn something, instead of having to come in on a certain day. 

You can also schedule a day that works best for you, when your day is free, therefore you would have nothing to worry about for the day other than taking the test. 

Also, people who may get test anxiety could feel more relieved when allowing them to schedule a time that works best for them in order to prepare properly rather than them having to come in on a specific day to take the test.

Making all students come in on a certain day makes the test feel forced and may make it harder for students to want to do it or stay focused. When taking a test it may already feel so forced and difficult and scheduling an appointment can make it feel less forced. 

When scheduling an appointment it can help you be more organized and put together. Being organized can also help students feel more comfortable and relaxed while taking the test. 

I feel as if scheduling an appointment is a better option when going to take the SAT.