Because later after a wedding shoot and you have over 700 images to sort through... you don't want to have to fix every image later! LOL!
I have been asked a lot lately how to control the Depth of Field in your photos and how to create a nice "Bokeh" (blurry) background. A lot has to do with aperature and also the type of lens you are using. Here is an image taken yesterday during a wedding ceremony. This image was left untouched by photoshop... straight out of the camera.
I used my Nikon D80 ~ Nikkor 50mm f/1.8 lens ~ ISO set to 800 ~ focus was on the diamonds
Here is the image after I did a noise reduction in photoshop and then sharpened only the rings. I then did a soft focus on the image. Not a big difference.
Now here I used some textures that I got from http://www.lovethatshot.com/. I used the Verona texture and then erased the texture from around the rings so that focus is primarily on the rings.
Very simple edit and took me less then 5 minutes to complete.