I'm not 100% up on the unwritten community rules, but they seem to prefer original content; because it keeps the search engines happy.

Re-posting your own work, while linking back to the original post, with proof that you control the content (like a message on the original post, with a link to the copy on steemit) seems to be an acceptable, but less desired, practice.

At least, that's my understanding, based on my interactions with people here, so far.