Legally your work is copywrited from the moment you finish it but if someone else steals your work and registers it you have to go to court and have strong proof that you created it. This will cost you lots of cash.
I am a songwriter and I have run into this and so have many artists I know.
The government wants your money.
I save money by bundling all the songs I have written for a year and copy write them. I will register a song individually if I think it is extra special.
This is my 2 bucks. Good article.