As you probably have noticed I have used HDR on several occasions now. I am slowing getting a sense of when to use HDR and when not to. Besides the obvious high contrast situation where the sky in a landscape would be blow out without some intervention - split ND filter, double processed RAW or multiple manually merged images - HDR when processed with Photomatrix has other advantages. First, if there is a lot of detail in a subject, the detail enhancer can really bring that out. For example, the tractor picture I published in an earlier blog. Or the image included here. As you can see there is a lot of stuff that grows on the trees in Oregon besides leaves. Generally I have not found straight photography does it justice, but HDR brings it out nicely. When shooting interiors, HDR is good for keeping hot spots from burring out - sun on a rug as shown in the second image. Finally HDR is good when you have an image that includes both interior and exterior subject material as seen in my earlier blog post on covered bridges.
I am sure I will find other good reasons for HDR, but these are a few.