Of course if somebody can get your server to display php code they'll see the path in your include/require and know where it is anyway, but it is a good idea to do so so that you do not have to rewrite the code ach time. For example I have a include file:
<?
$mysql_host="host";
$mysql_user="username";
$mysql_pwd="passwd";
$mysql_db="current_db";
$conn = mysql_connect($mysql_host,$mysql_user,$mysql_pwd)
or die ("Could Not Connect to Database!");
?>
That stores the connection variables and makes the connection that I just include on each script that needs access. The benefit to this is that I can give a client ftp access to their virtual folder and not to the folder where the db include file is stored. That way even if somebody gets into their folder they don't get the db info.