Cropping is an editing skill that has always been an important part of photography. It was widely used during the days of black-and-white photography and is now considered as an integral part of digital photography. Even though your frame is well composed during shooting, sometimes technical adjustments demands cropping. In digital photography, cropping gives you the power of reworking on your composition well after it has been shot. Modern editing tools come with cropping option loaded with presets of different composition techniques, rule of third for example. It gives you an option for deferring design decisions, and even let you explore new ways of organizing the photograph.
When you do stitching, you are combining more than one shot to make a larger image but during cropping, you are actually reducing the size of the image. This is very important point to remember if you are planning to crop your image later during post processing because cropping demands your original picture to be in high resolution if you do not want to loose the details in larger printing.
It is very common for the wildlife photographer to shoot very high resolution picture and later crop it to highlight the important part of the shot, eagle catching a fish or the head-shot of the bald eagle for example. Cropping is also being widely used to magnify the moon shot and most of the time it has nothing to do with the composition.
With the use of computer and advanced software, cropping process is becoming very easier and clearer. However, it is very important not to think of cropping as an excuse for not composing well at the time of shooting. You shouldn't let the cropping tool to become a habit of not being decisive about the composition during the shooting. The danger of creating such habit is that you start thinking that you can perform a significant proportion of photography on the computer and it introduces an interruption in the process of making a photograph.