I have been doing a lot of research on different breather/catch can setups. Most people run the lines from the valve cover to the breather tank/catch can. I know you can also run lines from the back of the block to a breather tank/catch can.

What are the pros/cons of either? What if someone ran both? When are they needed and when are they not needed?

This is a kit for the back of the block



This is the typical valve cover setup