the Preview mode is an undocumented experimental IPR mode, which changes the lighting and shading to gain navigation speed, so it is expected that it will change the look drastically, and may or may not work nicely (usually not, in my experience) depending on the scene
so if it happens to work ok for a particular scene, it can be useful to enable it while working on the model, but it is not intended for any final output
I tend to find it very helpful for texture deployment. While you won’t see the depth or specific light interactions, it’s faster and easier to see how mapped textures are going to function, without doing the full calculation.