Optical and Digital Preview

Just getting cracking with a newly acquired Pentax 645Z. I am struggling to fully understand digital and optical preview; the differences between them, which to use when and why the manual says I shouldn't use optical preview when using live view on the monitor. I have tried both digital and optical preview in live view (shooting in manual) and optical seems so much more straightforward. I would really appreciate the benefit of someones else's experience or technical knowledge with this. Many thanks.

Basically you can't get a digital preview in the viewfinder or an optical preview on the liveview screen.
Using the optical preview allows you to look trough the viewfinder and see the effect of stopping the lens down. In liveview the mirror is up so the only useful option is to use digital preview because you can't see anything through the viewfinder.
You can program the raw button to quickly switch between the two modes with just a single button press.

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John K

Thank you John. That's useful and, with the reasons, that's a lot more clear than the manual. Also, I'm ashamed to say, pretty obvious when I stop to think about it! I have programmed the Raw button to quickly move from one to the other mode, and now I understand why I would need to. Thanks again.