There can be no "official visits" until fall of the HS senior year, after Sept. 1.
All junior days are "unofficial visits". No free lodging or other travel expenses. Up to three free tickets to some game (football, basketball or baseball, whatever) for mom, dad and son.
The big advantage is not having your expenses paid. It's knowing that they are interested enough in you to have you come by early, and in getting the opportunity to speak with them face to face. When you're standing on their soil, unlimited talking is permitted. Lots of scholarship deals are offered, negotiated, even shaken on during these visits.