And to my good friend Phaz...Hoooow the hell do you have that many copies of these books?!
Mostly to give away or lend out. At any given time I probably have ~30ish copies on my bookshelf. That includes what I consider to be my own copies, those that are signed/numbered/ARCs/etc. Some of those have been read, many haven't. Then I have a stockpile of at least 1-2 of each of his books (in hardcover and paperback) that are just normal copies I can lend out. I tend to have a lot of dinner parties and things where people are over and we start talking about books. It's pretty common for someone to leave with one. Ideally I have a couple free copies of everything but have been getting short on some (like MB1). I don't keep any kind of list (other than mentally) of who has what book or exactly how many copies are out there, but that doesn't bother me. I just tell people to keep them if they want or better yet pass them on to a friend, then I pick up more as needed.
For instance about a year before TGS came out (but everyone knew Brandon was finishing the series) I was traveling and picked up a copy of MB1 for my trip (was doing another reread). I read most it on my trip, and after I got back I was going up the escalator after the tram (At DIA) and a guy noticed my book and said he heard Sanderson was going to finish WoT and was asking how good he was. I told him I loved Sanderson and MB was a great place to start. I ended up just giving him that copy because of how interested he was and knowing I have more at home.
Too me the cost of a book is often much much less than the amount of enjoyment I get from it (especially compared to movies and other forms of entertainment). I'll often just be in a book store and pick up a copy of a book I already have just to have one.
Like for Way of Kings my plan is to preorder one from Sam Wellers (to be sure I get a signed/numbered copy) and make the trip out to Utah for the BYU release (should be possible but there's always a chance I can't make it, hence the other copy). Then I'll probably grab 3 copies off amazon, one to read plus two to lend out, if those two go quick I'll grab one or two more.
A good portion of those books are also from something I did on the site Reddit. I love the community there and wanted to do something nice so I did
this. From my calculations based on the books I sent out, the people of those that said they had a friend/family member/etc who would read them and the people from the threads or who sent me a message saying they were picking up one of the books because of that, I converted over 100 people to Brandon, and that's just the ones I know about. I got lots of messages from people after they read the books who I'm sure will pass the joy on to their friends. That alone was over 60 copies of his books.
Brandon once compared me to being a drug pusher for his books. I'd say that's pretty accurate. When I find something I love, I share it with as many people as I can (both those I know and those I don't). Books are a big part of that but certainly not the only thing.
I plan on doing a similar thing for WoK when it comes out, and then another for The Name of the Wind a couple months before the sequel for that comes out.