Sometimes you need to redirect to the first child in your hierarchy, and the following can be put to good use for this:
http://doc.silverstripe.com/doku.php?id=recipes:controllers
But depending on how you customised your hierarchy with allowed_children arrays etc. this can sometimes wreak havoc on your page rendering. I found it easier in some cases to just use it as a function in the Page Controller class (give it a name like function goFirstChild() or something similar), and use the whole thing on a page-by-page basis with a CMS-checkbox-enabled If-block in your template, so you can use it on whatever page without having it load automatically as it does in the original version, if you know what I mean. Hopefully it helps someone, as far as I can see there's no downside to that.