diff --git a/doc/gundo.txt b/doc/gundo.txt
index e43620d..f047feb 100644
--- a/doc/gundo.txt
+++ b/doc/gundo.txt
@@ -210,9 +210,11 @@ Default: unset (windows use the default statusline)
 ------------------------------------------------------------------------------
 3.10 g:gundo_auto_preview                                 *gundo_auto_preview*
 
-Set this to 1 to rendering diff automatically with cursor move.
+Set this to 0 to disable automatically rendering preview diffs as you move
+through the undo tree (you can still render a specific diff with r).  This can
+be useful on large files and undo trees to speed up Gundo.
 
-Default: 1 (auto preview diff)
+Default: 1 (automatically preview diffs)
 
 ==============================================================================
 4. License                                                      *GundoLicense*
diff --git a/site/index.html b/site/index.html
index 1d28587..f86f143 100644
--- a/site/index.html
+++ b/site/index.html
@@ -332,7 +332,11 @@ let g:gundo_right = 1
                 <a name="gundo_statusline"></a>
                 <h2>g:gundo_[preview/tree]_statusline</h2>
 
-                <p>Set these to a string to display it as the status line for each Gundo window.</p>
+                <p>
+                    Set this to 0 to disable automatically rendering preview diffs as you move
+                    through the undo tree (you can still render a specific diff with r).  This can
+                    be useful on large files and undo trees to speed up Gundo.
+                </p>
 
                 <p>Default: unset (windows use the default statusline)</p>