hi lumone. This topic has been discussed before, but here is my short take on it:
Some schools value (almost require) visits for you to even have a chance of getting in, because they are often used as top candidates as a "safety" school. Therefore, for those schools, you'll need to visit and talk about it in detail in your essays or on the application. Schools off the top of my head like this are:
Haas, UCLA Anderson, NYU Stern, Cornell, Duke Fuqua, maybe Tuck and Ross. (I don't know about Darden and Yale)
Other schools value a visit, but people have gotten in without visiting at all. Going to visit will definitely help your case, but not visiting will NOT hurt.
Kellogg, Chicago, MIT, Columbia.
The Harvard, Stanford, and Whartons probably don't care if you visit or not. Some people have mentioned that Harvard didn't even have visiting programs set up for R1 applicants, but I could be easily wrong. Stanford has a visiting program, but I'm not sure they care at all if you visit, since their acceptance rate is so low, and they generally go for the "wow" type candidates. Wharton I'm not sure, so I won't say much about it.
Hope that helps!