As you move the cursor, your rubber-band segment jumps around and locks on to the selected line that is most appropriate. Object tracking need not be active. As with object tracking, you can unselect a paralleled or extended object simply by parking briefly on its marker cross. You can select several Extend lines and then find the intersection point between any two of them, but you can only be parallel to one at a time. You are not restricted to lines when determining parallel or extension directions.
Polyline segments work equally well.
And now here is the big one. All these examples use lines, and the AutoCAD Help facility refers to vectors, which implies lines. The truth is that these two new object snaps work equally well with any command that asks for point input. You can move objects in a direction that is parallel to an existing line, or you can copy a circle so its center lands on the extension of an existing line, and so on. And now for something completely different If you normally use a cordless telephone, make sure you also have a regular one available.