first time mommy and prenatal classes!

Cristina
Hi everyone!! So I am a first time mommy ( 15 weeks) and finally I am getting my enery and my appetite back!
 I have heard going to prenatal/birthing classes is a must, and some people say they are not necessary. 
What are your thought in this? And if you think they are really helpfull, when should I sign up?? 
Thank you so much!!!