I work primarily in design. When I've moved between companies I have been asked for this but usually at a final interview stage. I've mostly obliged as I like a

I work primarily in design. When I've moved between companies I have been asked for this but usually at a final interview stage. I've mostly obliged as I like a challenge, with the caveat that I have other commitments and so don't expect a gold standard in quality. My understanding after the fact was that this type of thing helped to identify people who were of an open mindset, the challenge put me out of my comfort zone a little too so that was another aspect. Finally it when the review happened it allowed us to talk about something we both had an understanding of. The only memorable time was when I identified some problems in their brief, ones they didn't notice, and called them out on it (not in a cocky way). This was the nail in the coffin for other candidates as no one else spotted it. Finally I've never been asked to do anything for an ongoing or upcoming project, only for something that had already existed. They also supplied content for me to work with and I chose what I could do with them in the context of what the role involved.