In a writing workshop you bring your latest piece of writing to class and people comment on it.
Since most people in a writing workshop are terrible writers, their advice is usually terrible. So you wait until the teacher comments on your work -- which is actually sometimes useful. So you end up with 24 mostly useless comments, and one mostly useful one.
So with Y Combinator I think they made the same mistake with group sessions in that you maybe have a Y Combinator moderator who knows startups and knows what they are doing -- and you have a bunch of other clueless people who mostly know absolutely nothing about startups commenting on your startup. Which is like trying to get a bunch of people who don't know how to play basketball trying to figure out from scratch a) the rules of the game and b) how to get the ball through the hoop. Do we kick it? Throw it? Get a ladder? What?
You'd probably get a lot more mileage out of forcing people to write 100-200 word essays each week and then posting all of those. And have Y Combinator guys pulling out the best posts and commenting on why they are the best posts. Or distilling recurring problems down into solutions.
Because getting at solutions from people who don't know what they are doing is great for networking, but probably terrible for Getting the Job Done In the Least Amount of Time.
Just like in a writing workshop. Where ten minutes of the teacher's time is worth ten hours of time from your peers.
MH