A few years back I got a used washing machine free from a guy that was going to take it to the dump. It's a high end Kenmore top loader and the only thing wrong with it was that someone had tried to wash a down comforter in it. The outer casing material had come apart and wrapped itself around and under the agitator. There were feathers everywhere. It took me an hour or so to get all the feathers out. I had to cut the casing material into pieces a few at a time to get it all from under the agitator.

I haven't needed to use it or even tested it but it was just too nice of a machine to end up in the dump because of someone's (fixable) mistake. But that's what can happen if a down comforter is washed in a home machine and the outer casing isn't strong enough for that type of cleaning.