Influencing Curves

Hi everyone, there is a question i have been meaning to ask for a while. When creating Boundary Blend surfaces, what exactly are influencing curves? I use this functionality almost every day, but have never used this option. I am wondering if i am missing out on a whole world of possibilities by not understanding what they are, when to use them, how to use them. There is very little guidance in the help centre. Does anyone have any good model examples or at least an explantion?

Regards

John