1. Definition of PS

It seems to me that when we discuss "PS" nowadays, most serious photographers are thinking about
"Normal PS"; while many others are thinking about "Extreme PS"

The best way to define "Normal PS" should be the commonly acceptable standard, or those accepted by
most prestigious photography competitions:

a. Cannot add anything

b. Cannot take out anything except dust spot

c. Cannot change anything (like making small object bigger, or big object smaller; changing color, etc.)

d. Allow: reasonable cropping, minor light and contract adjustment, minor sharpening

"Extreme PS" will be anything go without boundary. Obviously, that's not what we want to discuss here.

2. Can you get away from "Normal PS" while using digital camera?

The answer is no.

If you are shooting JPG, the camera is doing the "Normal PS" (without the cropping) for you when
converting the raw image to JPG. And this is the only option provided in Point-and-shoot camera.
In another word, even you are using Point-and-shoot, you are using automated, in-camera, "Normal PS".

There are settings come with DSLR that you can adjust to influence this "Normal PS" process. Many
of us completely ignore all these settings and use the defaults. However, they are there and it can
become handy if you need to calibrate your camera to compensate minor defect or meet your personal
taste.

If you are using digital camera and shooting RAW, you must perform the post processing yourself.

3. Do we need to consider PS when shooting?

For me the answer is yes and here are a few examples:

a. Push or pull. If you came from the film era, you should remember that if you push a role of
   film, you will mark the role and notify the lab when submit your role. The lab will add processing
   time when processing your film to compensate your push ("Normal PS").
  
   In digital world, you compensate that during "Normal PS".
  
   If you are not thinking about using PS at all, obviously you can never push or pull using your DSLR
  
b. Composition. When I shoot birds, due to the distance and the small size of the bird, I almost always
   have room to crop. So I can use the center focus point during shooting then using PS later to perfect
   the bird location. Of course, sometimes I do need to compose the object correctly during shooting
   when I can get "full frame" shots.
  
   If you are not using PS at all, you need to perfect the composition during shooting.

c. Recoverable range. There are often situations that none of the exposure setting can be perfect
   because bright area are too bright and dark area are too dark. In these situation, I will have
   to select the setting that I can recover the most during "Normal PS". These range are different
   among different cameras and post processing softwares.
  
   This is somewhat related to push and pull, but go one step deeper.