@jcalyst they're useful if you want the post to be discovered by other people (IE people who don't follow you, or are part of your local instance).
I've seen either way on the "put them in or at the end" (both arguments have been made by people who actually use screen readers!), so I'd say "put them into the post" if it works with the prose, or at the end if not.
In the case of intro posts it'll help people to find you when, say, looking at the "writing" tag,
@jcalyst And two more things that are hopefully helpful:
1) Try to WriteHashtagsLikeThis (camel case), since that makes it easier for screen readers to grok
2) there are groups for both writing ( @amwriting ) and fibre arts ( @fiberarts ), if you're interested =)