Belle is a pretty quick little dog, and although I am capable of bursts of speed, I am not capable of running fast enough to keep up with her over the entire length of a course. Lateral distance cuts down the yardage I have to cover considerably, but still in order for me to handle a course most effectively, I usually need to take some sort of lead out. How far I lead out depends upon the course at hand.
If the course has a fast opening, I have to take a long lead out so that my dog does not leave me in the dust. For example, if we were running the Tunnelers course below, I would lead out to at least the exit of the second tunnel with Belle. That way, I know I can beat her to the exit of the third tunnel and be in a position to direct her to the correct fourth tunnel (my prime consideration if I want to prevent an off-course). Additionally, I'm not so far ahead that I can't run and thus encourage her to run as fast as she can to catch me (my prime consideration if I'm interested in achieving getting the fastest run we can possible get).
Dusty needs no encouragement to run fast--it's part of who he is. If I were running this same course with Dusty, I would lead out to the exit of the third tunnel, face him and release him to the tunnels. My distance from him is cuing extension; facing him is my signal that he will be changing directions when he gets to me. (Sometimes this works; sometimes not so such.)
In my theoretical examples, my handling yardage for Belle is about 71 yards, and for Dusty it is about 10 yards less. Without the luxury of a lengthy lead out, my yardage would be increased by 10 yards for Belle and 20 yards for Dusty. More importantly in Dusty's case, I doubt very seriously I could get to a spot between the exit of #3 and the entrance of #4 in time to prevent the off-course because the faster you run, the faster your dog will run.