I haven't read all the 8 pages in this thread,
I have copied and pasted below, a recent entry from Brad Hill, about how to achieve a speedy route to see all preview files.
Hope it supplies a solution to some of the Cons that are being mentioned.
Most of those who use Adobe Lightroom for some part of their raw workflow probably know that Adobe updated the CC version(s) of Lightroom last week. In that process they split Lightroom into two versions - Lightroom Classic CC (for those in workflow with "locally" stored files) and Lightroom CC (for those working with images stored in "the cloud").
One of the things that has ALWAYS frustrated me with Lightroom is how darned long it takes to build previews (whether standard or 1:1, etc.). I typically had Lightroom build standard previews upon image import (to speed that process) but all that really did was delay the inevitable and slow down my image culling when I tried to view and/or compare images at 1:1 (as I waited for Lightroom to build 1:1 previews).
Anyway...for users of the new Lightroom Classic AND who shoot with the "latest" Nikon and Canon cameras you can cut this preview-building time to almost zero (really!). All you have to do is tell Lightroom to use "Embedded & Sidecar" previews when importing your files (you specify this in the File Handling portion of the Import dialog box). The embedded previews are those built by the camera itself and included within your raw files. Because the latest Nikons and Canons build FULL-SIZE embedded previews there is NEVER a need for Lightroom to take the time to build full-size (or 1:1) previews. So you can view previews of ANY of your images at 1:1 virtually instantly (i.e., right after import). And, when you do get around to culling your images and may want to view them at 100% (1:1) those previews are available instantly! Very fast. Very cool.
I have tested this feature with the Nikon D5, Nikon D500, and Nikon D850 and can confirm that each of those cameras DO have full-size embedded previews. At this point I can't say how many Nikon camera generations we can go back and still find that the previews that they produce are full-size. Sony, Olympus, and Fuji cameras don't produce full-sized embedded previews.
What if you want Lightroom-generated previews for editing (post-processing) purposes? Just go into Lightroom's Preferences dialog box and select the "General" tab and look for the checkbox beside this option: "Replace embedded previews with standard previews during idle time". And then check that box (it's unchecked by default). Because I process my raw files using Capture One Pro I have no need at all to replace those embedded previews with those generated by Lightroom (I use Lightroom only for image-ingestion and image management purposes including image culling, but not for image processing/editing).
Cheers...