How to Present a Case Study for an Interview

In one of the previous job searches, I applied for a role and got automatic rejection. And then I reapplied with the same CV, but I added a case study which I had prepared already for something else. It took me what, half an hour to rethink it a little bit. Sending in case studies when they're not asked for is a good way to kind of get that competitive edge in a previous job search.