Here is an example of where I have used the HDR technique to balance two photographs, one underexposed and another taken overexposed.  Here are both my original images:

Here is my final image after applying the HDR technique to it.

What I did was I merged 2 photographs together by clicking on: file, automate and then Merge to HDR Pro.  After this I adjusted my gamma and exposure settings and various other settings such as the vibrance and blur to add to the effects.  After doing this I changed the mode to 32 bit and adjusted the tones using the white point slider.  I then saved the photograph.  Here you can see the the photograph which is overexposed brightened up areas of the landscape and the colors and strength of the sky captured from the underexposed photograph are also present resulting in a nice balance of levels within the photograph.

Here are some other examples of how this works: