One of my biggest pet peeves is a glossy exterior brick wall. It looks so fake. How does it happen? Eggshell paint or a semi-mat, even mat glaze. It has too much sheen for an exterior brick wall. Bricks have no sheen. You can argue that an interior wall has been painted with a glaze, although its a weak argument, as I don't know that I've ever seen that in real life. So why does it happen... alot?
One of the reasons that scenics love to use a sheen in their wall finishes is the application of aging afterward. The aging treatments are alot easier to apply to a paint surface that has a sheen. It is alot easier to work with.
Another reason that they like the sheen is because the colour is richer with a sheen. A great example is the difference betwen a flat black and a slight gloss.
Its a trade-off. How important is the depth of colour in the scenic wall? My eyes are instantly drawn to the light reflecting off the bricks in the background of a film. When looking at an unglazed, flat scenic wall, I need to remind myself that the movie isn't about the wall.
I'd rather leave it flat. Good scenics can create good depth with colour. I'd rather forgo the rich depth of tone that would be attainable with a coat of gloss or eggshell finishes. Background scenery that distracts is a nuisance, and to me, colour depth is not worth distracting the audience over.