It's about where you want to go.
With the formula you can find any other position if you have some other information provided, such as the angle pointing at the other node angle(), and the distance().
Think of it as arrows pointing where to go.
With the behavior you get the positions already, but using the dist, or distance part of the formula you can say what distance you want to be at from that point with distance(node0.x,node0.y,node1.x,node1.y) being the max dist.
Using the indexing system of course.