I feel that Belle runs her fastest when I only take a short lead out or a lateral lead out. However, we also compete in USDAA and AKC, and sometimes the end of a course can be particularly complex. If it will save me enough energy that I will be able to do a better job with the complex finish, I will take a longer than needed lead out. Perhaps Belle won't run the course as fast as she might if I took a shorter lead out, but at least I will still be able to breathe at the end when I'm going to really need it.
Sometimes a lead out be the easiest way to avoid a tricky off-course trap. This is the opening from a Grand Prix course we ran last year. I lead out making sure Belle and I could see each other. I called and as she committed to #2, I began rotating so I could move toward the tunnel opening.
Many of the handlers who tried to run with their dog on their left ended up sending them to the wrong end of the tunnel, especially if they tried to get in a front cross between #3 and #4. Those who trusted their dog and did a post turn fared better since they weren't driving to get into position for the front cross.
This weekend, I experimented with doing a moving lead out. I leave Belle at the start line and jog away, releasing her as get far enough ahead. If you watched the video from Sunday, I am releasing her with a verbal "Okay" while I'm moving. She seems to find it pretty motivating.