Face Fillet Hold Line

Hey Guys,

I was recently watching a SolidWorks World presentation when the Hold Line feature came up. This seemed really interesting, but unfortunately the presentation didnt go into great detail about it. I gave it a whirl my self and was not really getting anywhere!

Basically, could somebody just break the feature down, let me know of any key rules, tips, tricks etc?

Thanks in advance.

SolidworksParts And Features