I would like to clarify a few points in this thread.
1 - Don't use case studies in your short answer. This doesn't help you, it only makes it harder to answer the question. You should be trying to answer the question succinctly. Adding in non-stimulus information only makes this task harder. Repear - DO NOT USE CASES FOR SHORT ANSWERS
2 - It is not just something to do to simply differentiate yourself from other students (i.e. band 5-band 6 students); it is actually a requirement for extended response questions (and by extended responses I mean the last question). The rubric quite clearly states that a case study / studies much be used. So dont take it lightly, you need to know one (or as I recommend - MANY!) otherwise your marks will be limited.
As for the business report, it is not required so in some ways I would recommend against using it, but it wont hurt. The problem with using case studies in the business report is that you are meant to be dealing with the stimulus not case study material. So for example you might be asked to determine problems within a business and recommend solutions. Your focus is not on case studies. Although you could for example say - "this was an effective strategy for this business, so it might work here" etc etc....