What are the advantages of publishing work in progress as a working paper? Some fields like Economics and Maths have their work in progress published as "working papers" with notes like "work in progress, do not cite or quote without the author's permission."Sometimes they upload these to their own websites or to their universities websites. I don't see much of this going on in my own field (sociology). I have heard from people that are afraid of having their work scooped or that fear that work published in this way will not be considered as "unpublished" by journals and conferences.

What are the advantages of making work in progress available in this way?
The advantages are that you get to stake a claim to some sense of ownership of the work; it's a way of inviting feedback and collaboration from others by showcasing your work in progress; and it's a quicker way to publish your work than submitting to a journal or conference.

So when do you publish your work as a working paper?

When the following conditions are met:


You've done some work.
And some combination of:

you want feedback on it from a wider group than your immediate colleagues;
you want to showcase your work to get new collaborators, new funding, or improved career prospects
you want to publicly stake a claim to the work you've done

And some combination of: 


the follow-up work is something that you've already got sufficiently far advanced that it is very unlikely that you will get scooped by your competitors;
you're not bothered about being first to publish the follow-up work yourself.

And publishing your work in a working paper won't prevent it from appearing (possibly in modified form) in a journal.