I have come across a few indie authors who do not make use of this free resource and I think it is a big mistake. Many readers use Goodreads to find their next book, basing their decision on reviews left by people they follow at the site. Some of these readers do not use other social media, like Twitter or Facebook, so Goodreads might be the only place to reach them.
Besides featuring your books with buy links, Goodreads allows authors to fill out a profile and make blog posts. I do not post there often, but I make announcements for such things as a new book release.
Of course, the more friends or followers you have at Goodreads, the better. I started out by sending friend requests to fellow authors and readers who have read books in the genre I write. I also review books at Goodreads on a regular basis, and the site keeps track of the books I have read/reviewed as a handy reference.
I know of one author who tried out a Goodreads giveaway at a cost of $120, and he did not find it to be worth the money. However, the free aspects of Goodreads are valuable and not to be missed!