$use_sub_dirs
Set this to false if your PHP environment does not allow the creation of
sub directories by Smarty. Sub directories are more efficient, so use them
if you can.
Technical Note
Since Smarty-2.6.2 $use_sub_dirs defaults to false.
See also $template_dir,
$compile_dir,
$config_dir,
$plugins_dir
and
$cache_dir.