As you know, HDR Light Studio let’s you put the lights where you want them in a HDRI map. This has been used to great effect with this render of a SLR camera. A small amount of blue was added to the light coming from the right which has given the image a much more 3D feel.
The reason why using a HDRI makes your renders look so real is that the light and reflections are in a perfect ‘union’ as they are being provided by the HDRI environment image. This is just like the real-world where a bright light can also be seen reflected by surfaces, and this is what we call a ‘high-light’.
If your CG materials have been set up with a photo-real approach, so without fake specular highlights, then the high-lights are generated from the reflectivity and roughness values for the shader. This will make your renders much more realistic when using HDRI environment maps, with sharp crisp highlights for glossy smooth surfaces and much more spread out high-lights being created by rougher surfaces.