For two reasons.
One: writing is quite a bit like acting. Your characters inhabit you, of course, but you also inhabit your characters. As you write them, you see the world through their eyes, acting and reacting as they would. For this reason alone, it seems to me, learning a bit more about how actors practice their craft can only benefit writers. How do actors access and express those parts of themselves that coincide with their characters'? How can you convey emotions and concepts indirectly yet effectively through body language, voice, pacing, etc.--all of which you can convert into words?
Two: at some point in your life, you are most likely going to have to read your work in public. And by "read," I actually mean "perform." For a long time, it has been something of a mystery to me why people go to author readings. I mean, we can read the book ourselves, right? So what's the value in having something read to us, especially in the rushed, hushed, even apologetic monotone that too many authors employ? Does having the words come out of the author's mouth really add anything to the story?
It can, if the author interprets the story through her performance. Now, here come the caveats: we are writers, not actual actors. We can't be expected to put on costumes and cavort around the narrow and labyrinthine confines of, say, a bookstore. However, we can learn to read from our work to help the audience better understand and--this is no small thing--more fully enjoy our presentation. We can learn to use pace, timing, eye contact, gesture (within reason), voice modulation, and other techniques to convey not just the words but the meaning of the story as we understand it.* This is why series in which actors, not authors, read short stories--such as Word for Word in San Francisco or the New Short Fiction Series in Los Angeles--are so damn fun.
And this is also why I've signed up for some private coaching from actor and teacher Valerie Weak as I prepare to read at various venues this summer. Having experienced just a single session thus far, I can say that learning to perform one's fiction is, first of all, exhausting. The level of concentration required just about drained me, to the point where I spent the rest of the day on the couch (not the casting couch, ha, ha). However, as I worked to inhabit, not just quote, my characters, I began to discover layers of emotional nuance in them that I hadn't actually been aware of. As Valerie told me, even small physical gestures can help you unlock the voice and meaning of the words--even if the audience can't see the gestures, which a podium might obscure. These discoveries alone have amazed and even thrilled me. I can now say I'm truly looking forward to upcoming readings, rather than mildly fearing them.
So, I say, fellow writers, get your actor on!
*Which is not to say that writers own the meanings of their stories, or that public readings serve the purpose of instilling a particular interpretation in the audience's mind. We're just offering some possibly helpful or provocative insights, which the reader can then respond to at his leisure.