If you own the content you can post it anywhere you want (even without spinning it), and you if you have a backlink in it, it will help the search engine rankings for the site that you're backlinking to.
But if you don't spin or change it significantly you will face two problems.
- Some article directories like ezinearticles will not accept the article unless it is completely original. They will check the internet in a similar way copyscape does to see if it's already out there somewhere. If they find it already on the internet the will reject the article for their system.
-The other problem is that if the same exact content is in multiple places on the interenet, the seo value drops. Google will index them but will not value all of them in terms of backlink quality.
As stated above, the best thing you can do is spin it or rewrite it and then use it in other places. If you are going to submit an article to ezine articles that is already on the internet, you should change at least every third word to make it past their checks.