As an “overseaser” who learnt in Israel I am on the hesitant side on sending away.
I saw a lot of my friends do things that wouldn’t do in there home town and not because their parents would get them in trouble but because they don’t have to be accountable at the weeks ends on what is really happening and how they look as over the phone you cannot really know what is happening.
I heard form a bookstore owner in Yeushlaim about a Bochur who came in and ask to charge his (fathers) CC and then he’ll take cash. He was ready for the store owner to take a nice chunk of the amount the main thing he’ll give him cash (as he wanted his parents to see a purchase in a seforim store & not know that he took cash…). What exactly he wanted to do who knows, but it was suspicious so he told him no way!
My humble opinion is, if you aren’t too far from home there is some kind of accountability as חברך חברא אית ליה וחברא דחברך חברא אית ליה & also if the topics does come up (not in a suspicious way he may very well see from his body language something and help out in the issues.
On the other hand there are many cases where the Bochur does grow immensely by changing environments and starting with a clean slate etc. but the above point needs to be address more than most parents think!!