Key thing to think about…
Each one of those little blue-lines represents a target position or shape for the mesh. (For all of the vertices of the mesh, all at once.) The essential purpose of RVKs is to describe morphing from one position, smoothly, to the next.
The closer the curve gets to one line, the stronger the influence of that position becomes, and the weaker the influence of the preceding position (line…) becomes. When the curve intersects the line, the influence of that position becomes 100%; the mesh “strikes the pose.”
Imagine that the various vertices of the mesh are being “pulled,” as if by various sets of electro-magnets, toward each position. There’s a wrestling-match going on between the previous position and the next one. As the IPO-curve moves away from one line, “those magnets are turned down” (becoming less powerful), and the magnets represented by the line-being-approached “are turned up.” The closer the curve gets to a line, the more influence that position has on the final shape of the mesh and vice-versa.
And so, “that is what those silly blue lines are for!”