When making the Sanchin Dai Ichi overview I posted last week we also made a more detailed explanation of the first few steps of Sanchin: from the beginning to the full double-underhook clinch. We call it "the Sanchin clinch." In our estimation it is the most important posistion in Goju Ryu because it's simple and it neutralizes an attack such that they can't get to weapons while you hold them. There are two "punches" invoved in getting to the posistion, but while they still hurt they are not fight ending strikes. The real damage is the position itself. It's very disorienting. The neck pressure builds up fast. The same posistion apears at the beginning of Sanseru, Sesan, and Superimpei. That's why I believe that this clinch is the default posistion of Goju Ryu. When attacked: try to get the Sanchin clinch. It won't always work, of course. That's why the katas don't end there. But if it does work it's a simple and effective way to stop a person hurting you.
Hope that makes sense. I'd welcome any questions, comments, nit-picks, or snide remarks. We're trying to make it as water-tight as possible so any feedback is appreciated. Thanks.