its bad for the company because the candidate can work with someone else and produce a glowing submission. I have helped a number of people do these some that have gotten the job.
its bad for the interviewee. They may spend 10-15 hours on this and get rejected for no reason at all. Do you think the person reviewing the submission is putting multiple hours into it. Doubtful.
If the intent is truly(and I mean truly) help individuals that struggle with traditional interviewing techniques then kudos. Demonstrate this by allowing candidates to interview in a way that is comfortable for them(including not taking your take home test) If its the company saying "my time is more valuable than yours. Do this assignment then we'll talk" then no thanks.