Location in WatchFast: File Menu -> Program Settings -> Misc
When this option is turned on, WatchFast will load in the files of the folder assigned to the Preset button that you activate as fast as possible.
If you have not noticed already, if you stretch the list of files on the Player window to the right, you will see four more columns: Size, Date, Extension, and Path. Populating the first three columns takes some additional calculations which can add up when thousands of files are being loaded. Those columns will remain blank when the Fast-Load option is on.
WatchFast doesn’t use the Size, Date, and Extension columns for anything beyond sorting the list. So, those columns being left blank will not harm anything. They are there so that you can quickly find out what your smallest files are, what your newest files are, etc.