This can make sense when you're doing batch requests and allow partial failures. I wish there were a standardized way of making batch requests--maybe even HTTP-level support. (It isn't such a big deal with HTTP2)
No, 206 is only used with Range requests, when you try to get only some of the bytes of a larger resource.
There is 207, I think created by WebDAV, where you give back an XML document detailing the status of sub-requests. I feel like that'd be confusing in many contexts as well, and a clearly defined custom response is probably easier to handle for the user.
