Some couples I met around the USA would actually want to see if their partners are great in bed before marrying. This is after many months of dating of course, but if someone out there in Indonesia founds out their partner is awful, this is going to be troublesome to live through that committed marriage.
In reality though, I only see this law as a way to enforce limited population growth, but it is almost impossible to monitor everyone, especially if Indonesia decides to get as far as banning protection from pharmacy stores, too.
Does this law apply to couples who visit Indonesia, who aren't married? I bet someone out there has a vacation planned for Indonesia, in one lucky hotel room.
