I think this is a good principle. It's easy to get confused about what a function is/does unless you have a guide. (For experienced developers, experience is that guide.) The samurai principle seems to be what functions were originally for... At least in the OO world.
Talking about Samurai and coding. I prefer Wil Shipley's take at <a href="http://www.wilshipley.com/blog/2005/02/free-programming-tips-are-worth-every.html" rel="nofollow">http://www.wilshipley.com/blog/2005/02/free-programming-tips...</a>.