Anomalum
We can detect thanks to IP address, e-mail address, username and other information. Of course, as with everything, there's no 100% guarantee, but at least there's a door as soon as you register.
With the current system, the door is wide open. And with this group solution, we add one or two doors. What's the point ?
Moreover, putting a message or discussion under review can confuse the member:
Why let me into the forum and block my messages ?
At least with registration under review, thanks to the e-mail, the member can understand that we're being vigilant.