Forgive me for asking a rather dumb question; my knowledge of colour management is limited. Also, forgive me for a rather long post, but I have to explain what I mean in my own terms, since I don´t have the "pro" terminology.
AFAIK, Lightroom B4 still uses the ProPhoto working space, and this isn´t user selectable. As long as it renders 12 bit raw images internally, no problem. However, when one either imports jpeg´s, or exports to PS for editing for web use, one has to fit the info into 8 bits per colour.
Now, since ProPhoto is a very wide space, most jpeg´s from simple digicams, and certainly not sRGB images for the web, can use the full gamut of ProPhoto, and so the representation of such images can use only a part of the full space of 2^(12*3) possible data points. Yet, this smaller, used part must be transferred to the space of 2^(8*3) possible points, and I have a feeling that this is somewhat similar to enlarging and cropping a negative where the subject doesn´t fill the frame: there are quality losses.
If this is correct, wouldn´t a smaller working space, like the Adobe RGB be more "efficient" in this respect; it uses the same 2^(12*3) possible data points to represent a smaller gamut, and so a given image would "fill the frame" better, so to speak.
And now, finally I´ll try to get to my question: If I am right, won´t the risk of posterization in the shadows actually be greater when using a very large working space and then converting to 8 bits in a smaller one, like an sRGB jpeg? And if it is so,
1) wouldn´t it be a good idea to be allowed to select the final, small space already when exporting to PS?
2) wouldn´t it be a good idea to allow a user who has to work with lots of jpeg originals to select a smaller internal working space within LR.
Photoshop allows the user to do both, and PS and LR are both Adobe products. So, why no choice in LR? Is this a non-problem in practice, or (horror....) have I got it all mixed up?
Edit: I see now that if I don´t select "Edit in PSCS2" in LR B4, but instead just "Export", I can select both file format and colour space. While it is a more roundabout way than going directly to PS, it does take care of my point 1) above. Still, I see no way around 2).