Hopperhop, good question and you most likely will get a variety of answers.
Official visits often mean that the coach is very interested in your son. It's his chance to get to know the players, and your sons cahnce to get to know the staff and team and view the facilities, talk with the academic advisors. A chance to get a "feel" for the school with student population. If it's a football weekend (assuming ther eis football), it's an added bonus.
Not all official visits turn out to be successful for both coach and player. I know many of players that declined offers after their visits.
It's tough when pressure like that is put upon a player, and sometimes that pressure works negatively in the recruits mind.
Mine went on two official visits and was expected to verbal at each one, he didn't and opportunities were given for more time to decide. Yo never know what will happen.
Approach the official visit as an invitation to learn as much as you can, if forced to commit and it doesn't feel right, then don't.