Understanding ACES and ODT

Spectral rendering or Rec2020 gets one closer to ground truth in terms of colors, compared to say; sRGB / Rec709 ?

Therefore if one has a display which can display around 85% of Rec2020 would it not be best to set that display to Rec2020 even though some clipping will occur just to get a better representation of color compared to sRGB and Rec709 at 95-100% accuracy ?

Also the reason why it’s useless to use AP0 primaries is because one will waste the colors that are used because the gamut is too big over AP1 primaries, correct ?

In what context do you mean exactly? If you are creating a product for SDR displays your monitor and ODT should be set to that. I’m pretty sure that a display capable of 85% Rec2020 can accurately be hardware calibrated to it with Delta errors less than 2. You could set a display to native gamut but then you become reliant on the software managing the conversion in the case you want to view an sRGB image which you can’t do if it is not tagged or supported by the software.

Doing it on the display side of things removes that uncertainty because it can be calibrated and validated.

I think there are two main reasons. Encoding efficiency and grading predictability. Covered a little bit here. Difference between Virtual and Real Color Primaries - #3 by sdyer

I was informed it’s pointless to calibrate a display which can only do around 85% of Rec2020, although you say otherwise that one could still benefit from such a display.

No commonly available display can cover 100% of Rec.2020. But that is not normally an issue, because most image data (at least for deliverables) which is notionally Rec.2020, is in reality a Rec.2020 encoding of image data which is limited to P3-D65 – a half pint in a pint glass, so to speak.

Would you suggest to still calibrate a Rec2020 display even though it can only do around 85% ?
Also how could one know what colors are being clipped for that display ?