Setting may seem like a simple backdrop where your plot unfolds, but it does much more than that when handled with care. It sets the tone and adds perspective into your characters' lives.
Whether they are city dwellers or country folk, describing the setting allows readers to relate on a broader scale. No one exists in a void. When I say I'm from Colorado, for example, people subconsciously--in miliseconds--create an image of what that means to them. They may picture mountains or craft beer...skiing or hiking...all from a word. Whether or not any of these things are actually connected to me will only be revealed after knowing me better. So it is with the story you wish to tell, whether it is nonfiction or fiction, where your story takes place is essential to the reader's understanding.
But too much description slows down the pace, you protest. I agree that it can if it's overdone. As with all story elements, setting must be woven into the plot with balance.
But you say treat setting like a character...what exactly do you mean by that? Think about the setting's personality. Every place on earth has a 'feel' to it, an unique vibration, a tempo. It's not enough to say simply "Colorado"...what's around me? What are the people like? What does it smell like? What does the air feel like? What are the local foods? How does being in Colorado affect the characters? Why are they here? There's a reason that you, the author, chooses a particular setting. Why is your story there? Will the elements impact the plot? Does it shape the characters' habits?
Give setting as much thought as you do plot and character development. If you're setting a suspense novel on an island, for instance, that immediately amplifies the tension. Where do you run if you're on an island? Where do you hide? How does the ocean sway your characters' decisions?
Even if you do not write it all in your story, think about these questions while you're revising your manuscript. Is there a balance between describing the setting, unfolding the plot, and defining your characters?
In order to have a fully fleshed out manuscript, the setting needs to come alive in the readers' minds. Let them feel the heat or the cold or the isolation. Let them hear the noise or smell the trash. Allow your setting to weave into every scene in such a way that you transport the reader into your world.