Share 'Giveaways - What's the deal?'

I see many blogs that offer book giveaways and since I'm new to blogging, I wondering if they are necessary to keep blog readers and/or grow readers/followers. Are they? When you are just starting out blogging, how do you get books to give away? Is there a way to best promote book giveaways? When it comes to author interviews along with book giveaways, do you contact the author first? Or contact…