[Elecraft] Filter Question

[Wilson Lamb]

Would someone please explain the relationship between our plug in filters (K3) and the variable filter response provided by our width control.
As I understand the situation, the plug in filters we buy are roofing filters, used to prevent intermod from strong signals outside the pass band.
Is there more to it?
If there were no other signals, would the width control work the same with and without the plug in filters?