So every time you convert to DNG you’ve been checking the option to include Fast Load Data. Anything you can do to speed up “walking images” (moving from one image to the next in the Develop module) should help, right?
Over time, you’ve also correctly discovered that rendering Smart Previews speeds up walking images. When Lightroom sees that a Smart Preview is present, even when the full RAW/DNG file is available, it will load the Smart Preview into Develop first and “light up” the control sliders, then continue silently loading the full file in the background. The result is the appearance of faster image load times.
Under these circumstances, the Fast Load Data is completely redundant. The presence of the Smart Preview provides 100% of the performance benefit of the Fast Load Data, plus some additional performance. In fact, when a Smart Preview is available, Lightroom completely ignores the Fast Load Data, so it provides no benefit at all. If Smart Previews are a normal part of your workflow, you can stop embedding Fast Load Data, and save both a little bit of file size, and a little bit of DNG conversion time.
Do you use Fast Load Data? Smart Previews? Neither? Have you been using both? Comment below.