I ask myself this every time I post on my blog and feel every writer should too. I have posted links to already published work and a little teaser of a story or some poetry I do not intend to sell, but I'm keeping my story sharing to a minimum for a few reasons.
1) I want to sell stories. If I post everything, I'm writing for free, no one will have a reason to buy my work.
2) I already post my works in progress on a critique forum and feel that forum is the professional choice for feedback from peers. I want to put forward my best image on my blog. You never know when someone important in the industry will stop by and I don't want my unfinished work to be my first impression. I only get one chance to make a first impression and it's going to the best one I can!
3) I am concerned with copyright issues. If I post something here, technically, it's the first publication. I want my work published for the first time in a publication other than my own blog.
4) Even though this blog is copyrighted, I know there is the smallest chance someone reading my work would try to steal my ideas. Unless you're Kim Harrison or another big name, you might never find out someone stole your work, unless you or a friend stumbles across it by chance. I am very careful about what I share and with whom.
My advice to writers is to share only short teasers of your work or links to already published writing. If you just want to share your writing with the world, then publish wherever you want, and please, leave a link so I can enjoy your stories too. But if you're trying to get a agent, get published, and are in the business professionally, consider what I've blogged today.
As always, happy writing and happy reading to all!