diff --git a/site/docs/usage.md b/site/docs/usage.md
index 6db3a112..6f5c9a3b 100644
--- a/site/docs/usage.md
+++ b/site/docs/usage.md
@@ -24,6 +24,17 @@ $ jekyll build --watch
 #    watched for changes, and regenerated automatically.
 {% endhighlight %}
 
+<div class="note warning">
+  <h5>Destination folders are cleaned on site builds</h5>
+  <p>
+    The contents of <code>&lt;destination&gt;</code> are automatically
+    cleaned when the site is built.  Files or folders that are not
+    created by your site will be removed.  Do not use an important
+    location for <code>&lt;destination&gt;</code>; instead, use it as
+    a staging area and copy files from there to your web server. 
+  </p>
+</div>
+
 Jekyll also comes with a built-in development server that will allow you to
 preview what the generated site will look like in your browser locally.