Many people, when trying to persuade others that reading for pleasure is useful, refer to the wonders it does for your vocabulary and your spelling. But these reasons are not the main reasons I would encourage people to read. Books are full of peripheral information. In order to describe something well you need to know what it looks like and feels like and sounds like. If you are talking about animals, you need to know how they behave. The same goes for organisations, although sadly, not always for people. This comes through in the book. A book well researched is a book full of life. Even fantasy novels work better if the author knows at least something about the dynamics of semi-medieval society, or how weapons should be used, or whatever it is they are basing the fantasy. In historical fiction you learn an enormous amount, as long as the author has checked their facts (and usually you can tell). Simply reading novels can teach you a lot about the world.
Not only that, books stretch your ideas. More intellectual authors, such as Terry Pratchett, include a rather healthy dollop of philosophy in what they write. Books such as Jostein Gaarder's The Solitaire Mystery introduce new ideas in a shape which fits into anyone's head. Books have caused me on so many occasions to question the nature of "life, the universe and everything" that such questioning is part of my approach to the world. Even books without philosophical intentions provide additional perspectives of the world. On the simplest level, they illuminate the opinions and unspoken assumptions of previous generations. Looking deeper, attitudes of different religions or ethnic backgrounds can become familiar and understood through novels.
Even more important, to me, are the phrases. Books give you words with which to write the world. Every so often, while reading, a phrase emerges which stays in your mind for the sheer recognition you felt when you saw it - a phrase which perfectly describes what you already know but have not found the words for. You come to a greater understanding of your own ideas by hearing them described.
Sadly, few realise that enjoyment of literature is more than a way to broaden your vocabulary and improve your spelling. How many, when asked, could think of more than utilitarian reasons for literacy? So while we, the lucky few, curl up in a corner of our favourite library with something familiar or something new, those who do not share this joy may never know what they're missing. Books are food for the soul - and as with all food, there is cookery and cuisine, sweet and savoury, sustenance and luxury. So I will not encourage people I meet to read for the sake of their vocabulary - that is why the thesaurus came into existence. I will encourage them to read because they'll never what they were missing if they don't.
A Piece of String: The ramblings of a philosopher (in the old sense of the word)
