I've revisited the log-line as a tool used in script writing, and found a new appreciation for it. Now, I find that it is a powerful tool in developing stories. In general terms, a log-line is the brief summary of your script, compressing the whole work down to a few sentences at most, detailing what the script is about. Here's an example from a script I wrote:
"Jack, a psychiatrist, goes on a journey searching for his lost pen."
I've found that during the writing process, when a scene is weak or disjointed, that often indicates that it does not adhere to the log-line. Thus, losing the scene, or else refocusing it to fall on the log-line is the answer, or at least a way to re-conceive of the scene to improve the script.
This is especially helpful in the developmental stage of writing, where the story is still emerging. On my latest project, it has helped me jettison some scenes, and re-focus another sequence that was dangerously on the fringe of my story world. One more example:
"Jerry destroys his life through his obsession for retribution towards a telemarketer’s nightly phone calls. He loses sleep, his job, his girlfriend and his freedom."
