Chefs keeping copies of the recipes they came up with for their employers, screenwriters keeping scripts, authors keeping early drafts, musicians keeping sheet music, photographers keeping prints (if not negatives), any job where someone is expected to keep and maintain a portfolio
Good examples, I seriously could not think of any.
The difference I see is that those are works that are produced on ones own and then sold to buyers (except maybe the chef, I'm not familiar with that area.) Code, in the above context, is not created first and then sold to the business (unless its code/software one own in the first place). It is work that happens after a problem arises and then one is hired to provide a specific business domain solution.
