With a bigger group there is more time to unpack the problem. There is more time to hear students thinking, and to help students understand each others thinking. There is also more students to share their thinking, so therefore a bigger pool of ideas.
This is possible because of the way we run our modern learning environment, where most of my maths class are working at about the same ability level.
The challenges of this is I then have a much larger group to manage while on the mat. It also tends to mean I have that group on the mat for much longer than normal, which can run the risk of losing student interest.
Not exclusively Super group
Although these students know they are one big group, they still are split into normal smaller size groups as well. This is because I don't necessarily exclusively take super group sessions and will sometimes switch back to the normal size groups. It also means I have the option to dictate what specific follow up activity I want the two groups within the super group doing. That way I don't have to have half my class doing the same follow up activity at the same time If I don't want to.