I would like to engage in some speculation. I have a very strong feeling Sanchin Kata, was designed for a definite purpose, not just for health reasons. I think it was in part designed to develop a defense for a most common Okinawan type of attack. Not from foreign warriors, but from the ever prevalent Okinawan people who might engage with a most Okinawan type of attack.
Nagamine Shoshin details this art in his book “Tales of Okinawa’s Great Master’s” being the art of Tegumi. The most popular Okinawan sport of Okinawan Shima, which almost every youth would have tried and was a most popular sport.
Then back in 2011 I saw a discussion about Sanchin Nukite Thrusts by Jim Prouty on Bill Glasheen”s site at http://www.uechi-ryu.com/forums/viewtopic.php?f=11&t=21479
Jim wrote , “Many folks treat the nukite as strikes to the body. Yet, if we accept the premise that Goju means "hard/gentle' or is a study of opposites, many folks dismiss the pulling action of the arms as being important. In this case, the hands close as in a grasping movement, the next action is that both hands turn in a pulling action; it is this movement that I suggest to my students is a skin grab of your opponents side. Which is extremely painful. Here is an old photo of Miyagi Sensei performing an omote or gyaku bunkai to Miyazato's attack. (This application is found in several Goju kata):”
At the time I saw this as simply a great application.