If you are very interested in a school, but have to choose between visiting before sending in the application or right afterward (during the review period), does it matter? Will admissions know and record that you visited if it is after the application is submitted?
If your schedule allows, I would visit before submitting the application. Your child may hate or love the school. If he/she hates it, you save the fees and the time and effort in applying. If he/she loves it, it might give him/her more inspiration in writing the school specific essays. To the extent that a school even tracks interest through campus visits/tours, I doubt there is any difference between a pre and post application visit.
We did all the visit before my D’s college application and return to one after admission.
Depends on the school. Some colleges value demonstrated interest and visits are a great way to show interest. You should google the common data set for each school you are interested in, look at section C, and see if demonstrated interest is part of the admission decision. For schools that value demonstrated interest if you live close enough to visit before your application is due that would be a positive (perhaps also try to arrange an on campus interview if they are available). If you can’t visit there are other ways to demonstrate interest (ex. sign up on email list, ask for an alumni interview if available etc.).