I didn't bring anyone to the ASD that I attended, but most people did. I might have brought my husband, but he had to work.
I think it depends on how your guest will act. In my experience, SOs are better to bring than parents. This is just because from what I saw, the SOs were good about letting the student make their own impression on people. They generally didn't ask too many questions or talk over the student. Parents definitely did. Moms would answer questions for the student instead of letting their kids talk. It really made the students look inexperienced and young.