Are songwriting classes necessary??

I did not even though there were classes for songwriting (it is like taking a class for learning how to tie shoelaces). I thought with songwriting it was just something that came to you at unexpected times. What exactly do you learn there? Is this just a class to make more money? I've been writing for quite a while and I've never taken any classes, but then again I'm 17 and have never shown anyone songs I've written because of the worry someone else would steal/copyright my song.