To add to the chorus...
With nikyo my goal is generally a structural control. Like most things we do. Sometimes it hurts. Sometimes I might even want it to hurt to emphasize a point (Peter R's inner sadist). It just depends on a larger context that is itself rather resistant to absolute and simplistic discussion on-line (and I don't mean that to sound dismissive, simply that it "ain't so simple"). Shrug.
I should modify this a bit and say that the structural aspect is one that if it is fought against tends to result in pain, especially in those who don't know how to work against it.