Your dog might have special health issues which require you to shop for her dog food by need.
Things to consider: Diet needs for special conditions, temporary health changes, and nutrition for active dogs.
Permanent Health Conditions - If your dog has allergies, you are going to want to make sure that her diet does not aggravate her systems. In this case it's best to shop by need.
Temporary Health Conditions - When your dog is feeling sick or is recovering from a medical procedure, it might be easier on her system if you shop by need and feed her a bland diet for a little while.
Pure Energy - If you have a highly active dog, shop by need. An active dog needs a higher performance diet, usually higher in calories (among other things) to help supply her energy she needs to suit her active lifestyle.
