The first fundamental difference from the usual group discussion is that 1-2-4-All gives everyone present an equal opportunity to contribute. All the silent thoughts that otherwise would stay in people’s head can be spoken out loud, starting with the individual reflection time, a rare opportunity to collect one’s thoughts without disturbance.
Moving on to a pair formation provides as safe a space as possible for each to articulate these thoughts for the first time, get feedback and hear one other person’s point of view. Creating safe spaces for expression (versus asking people to take the risk of speaking up in front of a whole group that almost always includes someone with more positional power) transforms both the amount and, most important, the diversity of ideas expressed.
After the second step, ideas, especially those controversial ones, can be more safely presented as emanating from a group rather than a single individual, thus liberating many views that otherwise would never come to the surface.