It's not mandatory but it's a good idea for many reasons:
- If done prior to admission decisions being announced, it can help demonstrate to a prospective school that you're sincerely interested. They want the students they select to accept and enroll. A visit can help convey to them that that's more likely to happen if they accept you.
- There is no substitute for being there in person to really understand what it's like. Hearing about a school, looking at it online, talking to others about it...those are all helpful. Those should help you narrow the choices. But there are things that you can only discover in person. What appears to be your top choice might suddenly drop down the list and conversely another might make a big jump to the top.
- It helps the student get a sense of the type of school they're looking for. Big, small, spread out, compact, middle of a large community, more remote. Again, the best way to understand is to be there in person.
- Would you move to a new city, possibly a new state for 4 or 5 years and not visit first?