Do you love browsing aisles of books? Could you easily spend an hour or more in a bookstore? Then, it would be to your own advantage to buy your books there.
I hear horror stories from the proprietor of my local store. "Customers" come in and ask to photocopy parts of books (rather than buy them) or say they are looking for books they will later buy online! They don't even seem to realize this is rude...or that the owner is struggling to make a living.
Bookstores are going out of business right and left. If you want the luxury of visiting a bookstore in the future (whether it's a Barnes & Noble or a small, local store), you should buy at least some of your books there now.
If not in stock, any book available online can usually be ordered. And it will usually arrive in one to two days -- with no delivery charge to you. When I know what book(s) I want, I call my local store to order them. They let me know if they are in stock, or call me when my order arrives. Very convenient!