Ever find the perfect journal article on your subject, only to be totally confused by what it's saying? Books are the answer to that problem.
Because articles are shorter, they don't have space to explain everything. Books usually give you more context and background, making a subject easier to understand.
MeL is a great resource for getting books that you can't find at FLITE. You can search and request material from other libraries and have it sent to the check-out desk at FLITE.