Personally, I would never do sample work, but perhaps I'm not the target candidate.

I've been working remotely for ... 8 years now? I've worked for startups through that time and it's always been companies that were already aware of my work.

I don't think I'd ever go through a proving process, but I've been doing this a long time. Perhaps for someone new, it makes sense to do that.

To me it feels insulting, and I've heard stories from friends that they've done sample work that has been used within the company, but they didn't get the job.