I think it's pretty much unnecessary. The rating is there to show what other people think about the quality of the content. If the author him/herself would rate the own piece badly, he/she probably shouldn't put it online. And since it was put online, it should be good and therefor the author doesn't need to underline it with a good rating.
Also... I think most people believe the ratings are from other users, not the author. So if you push the rating of your own content, it's kind of like pretending that more people liked it (because you probably wouldn't rate it low) than really did. Even though you don't get point for those ratings, it can be considered cheating, because you influence the outcome of the ratings (the average).
So: don't rate your own stuff. 
Regards,
Steffi