When theming a view there are two approaches, in a template file or rewriting field output, what are the advantages and disadvantages of each?
You would want to use a template suggestion as they are called for small modifications to the design or DOM output adjustments.  You will use this %90 of the time.

rewriting field output should be handled by hooks EXAMPLE: if you are taking a value and turning it into an image for rating display.... 

Use pre-processing hooks when you are applying logic to output values.
Use theme suggestions when making adjustments to layout structure.