What exactly does DNG conversion option "Embed Fast Load Data" do?

[jbinco]

I have not been able to find any documentation explaining exactly what the "Embed Fast Load Data" option does when converting to DNG.  Can anyone enlighten me on the specifics of this feature?  The standalone DNG converter and the tool tip displayed when hovering over the option in Lightroom note that file size will be increased.  So what is the cost/benefit of this option? 

[johnrellis]

From the help:

https://helpx.adobe.com/photoshop-elements/using/processing-camera-raw-image-files.html#save_changes... 

Embed Fast Load Data: Embeds a much smaller copy of the raw image in the DNG file, to enhance the speed at which the raw image is previewed.

[TheDigitalDog]

DNGs with Adobe software will load faster when there is an embedded preview image called Fast Load Data (FLD). In other words, the benefit is improved performance. Since the data is embedded in DNG, that means it travels with that DNG file.  Wherever you send the DNG, the embedded FLD is always available for helping performance.

[Ian Lyons]

To avoid confusion - it's 'only' used in the Develop module where it serves the same purpose as the Camera Raw cache file used by proprietary raw files (e.g, NEF, CR3, ARW, etc).