Only been using it a few weeks, and already it's saved me days in minutes. To clarify:
You buy a WP theme—a mediocre one or a gone one, let's say a good one—and you have to locate something simple, which is of course buried in includes/functions/variations/youllneverfindthis.php. You spend 30 minutes tracking it down, after which you have no energy to do the little thing you meant to do when you started, so you do something else for a while, and postpone the little thing till tomorrow.
What the File cuts out the search, and thereby cuts out the day. See? Days saved in under a minute.