Chris Lee at arstecnica covers some academics who are trying it
When this approach was tested (with consent) on papers submitted to Synlett, it was discovered that review times went way down—from weeks to days. And authors reported getting more useful comments from their reviewers.
The forum is open, so as a reviewer, you can see comments accumulating, and you know the editor is going to close comments at some point soon. You are either going to do the job now or not do it at all—you can’t put the editor off for three weeks before deciding that you don’t have time.