I think the biggest reason for both boys and girls is for them to experience the types of families who live on a whole different existence than those in the US. The yiras shomayim and idealism is something that you can only absorb by living with such people for an extended period of time, going to their house for shabbos etc. It is immersion in that environment which can have life-changing effects (although it is not automatic). There are no metrics for what I am talking about. Either you get it or you don’t.
The second-biggest reason to experience E”Y not as a tourist but as someone living there. It’s the kind of thing you can do by staying in a hotel for 10 days and going on a tour bus.
Obviously one needs to understand where your kid is holding to determine if the risks are worth the possible reward. Giving some kids independence without supervision can be negative.