I have recently been doing lots of reading, in genres ranging from romance, to fantasy, to historical fiction, to religious nonfiction. (Now that's variety.)
The nice thing about reading for pleasure, for a writer, is the opportunity to switch mental gears. We are now on the other end of storytelling, as a reader. The switch is no longer complete; as a reading writer, I find myself noticing editing errors or plot transitions more than I used to. But it's still a nice change to dive into someone else's world for a while (or in the case of nonfiction, expand my horizons).
Reading does writers some good for their own work - especially fiction, if you're a fiction writer. (I imagine reading nonfiction does the same sort of thing for writers of nonfiction.) I tend to notice good characterization and dialogue much more, as a reading writer. The things I admire in others' work are often the ones I'd like to strengthen in my own. It helps to see how other storytellers approach these challenges. Reading also has the nice side effect of being a mini-vacation - so I'm refreshed and ready to work again once I get back to my own stories.
So that's why teachers of writing tell you to read, read, read. Good for your mind, good for your soul, and just plain good fun.