Asking that question is Mark O'Connell at The Millions . He makes a good point: it is kind of ridiculous how seriously people take these things, how offended people can get if their favorite isn't chosen. There's no way for one award to please everyone, to choose the one book that is truly, objectively the best--there is very little "objective" anything when it comes to art. However, for librarians these awards are pretty indispensable. You'll see plenty of posts on this blog, for example, about winners and shortlists. We use them when deciding what to buy, what to recommend to people, what to read ourselves. Maybe it would be better if everyone read all of the books and judged every one for themselves, but that's never going to happen.
So readers will look to awards lists to tell them what's good, and librarians will look to them to tell them what readers will want. That said, you have to learn to be a little bit leery of these lists. There are a ton of awards out there, and not all of them are that selective. Even when they are, if they have a narrow purview they're liable to at least longlist everyone in their genre. I write reviews for Booklist and Publisher's Weekly, and it seems like even the Booker's cachet is rather dilute--every other book I get (granted, I review literary fiction) seems to be by a "Booker-nominated author". And of course, as O'Connell points out, there's no accounting for taste. The judges of even the most prestigious awards are still just people, with their own idiosyncratic preferences. Rarely are they completely off base, though, and I have to think that, overall, it's a good thing to get people reading and talking about quality books in the way these awards do. In that spirit, here's the Booker longlist  that inspired O'Connell's article, and a few highlights that MCPL has already ordered or received (with links to the catalog).
On Canaan's Side , Sebastian Barry
Jamrach's Menagerie , Carol Birch
The Sisters Brothers , Patrick deWitt
A Cupboard Full of Coats , Yvette Edwards
Pigeon English , Stephen Kelman
Snowdrops , A.D. Miller