I once used a couple of specialist apps to process some data. It turns out that they would put some data in alternate streams. I don't know exactly what they put in the streams, but they were all corrupted when I restored them from a zip backup.
Yes. It was questionable design on the part of the software designer and he was probably experimenting with one of Windows' new features. The point of "alternate streams" is to allow a file to look more like a folder to an app which understands them - effectively, a single file can contain multiple sub-files which are accessible by name. To the OS in general, the file appears as a single entity which can be copied and moved, granted permissions, etc. as a single object. The problem people have had, and why they have generally fallen out of favor, is that lots of older backup/archive software doesn't recognise them and doesn't preserve the alternate streams
Yes, these days, it's mostly only used to store download location information. But, I didn't know I needed this feature, and ended up boned because of it.
You're right about multipar/quickpar/etc. However, it's another piece of software, which if you're distributing data to someone else, they need to have a copy, and they need to know how to use. Plus several versions of quickpar are known to be buggy and produce "defective" parity data (i.e. the parity data does not provide the expected redundancy; it often provides none at all).
It really simplifies distributing data, if you can make a self-extracting .exe with a recovery record. It almost always works on the other end, and it saves the occasional delay if the CD or whatever media is slightly corrupted.