There are a number of things I don't understand well and this is one of them.

What is the full purpose of a push-pull fan design around a rad? If anyone can even just point me to a post about this that would be great.

Also if using a push-pull design do you need to use a shroud? What are the benefits.

I guess I am just looking at a run down of how it compares to just running fans on one side of a radiator and how it necessarily helps and/or how much of a benefit you actually see from running this kind of set up.