Does a fill flash actually help bring out detail?

I posted another question which sparked a bit of a discussion in the comments. Basically, in a high contrast (high dynamic range) picture, if the difference in distance from the camera to the different parts of the subject is negligible, then does a fill flash actually help bring out details in the darker areas of the subject?

The way I see it, if the difference in distance is negligible, then using a fill flash will add a uniform amount of light across the entire subject. If different parts of the subject are considerably but not extremely different in ambient illumination (say, something like 4-5 EV difference; as an example, in shade versus sunlit), this should help bring out details in the darker areas, since those are illuminated more by the flash relative to the ambient light level than are the highlights. But it's been argued in the comments that that's not the case, since the absolute difference in illumination remains the same with or without a fill flash (which would mean it's all about the exposure settings).

So, which is it? And why?

Answer

Michael, you are mixing two different things here. In the previous question we were discussing the effectiveness of using fill light to distinguish areas on the subject. Traditionally, a fill flash is used to bring a subject's brightness level to be less contrasty with the background, such that metering for the subject will not blow out the background, and metering for the surroundings will not underexpose the subject.

So, the answer to the question is yes, fill flash certainly helps bringing out details of a subject over a bright background.

EDIT: reading the comments below, I think I need to clarify the terms I use in this discussion. By referring to dark and bright areas on the subject I mean dark colors (i.e, black) or bright colors (i.e, white). Think Dalmatian. The argument in the previous question was that shedding light on the subject will not reduce the dynamic range of the light reflected from the different areas. Through the comments there one can see that a conclusion is that given multiple lights, then increasing one source's intensity can indeed reduce the DR.

In this question, the OP asks about the effectiveness of fill flash, and here, the problem is not the DR of the subject, but rather the whole scene.