Received a Thick DWP ESA Form ESA3 (IBR) To Comple

Good Afternoon Panel

I just received a thick form from DWP regarding my ESA claim and I panicked. You see, my re-assessment ESA WCA is not due for a few months.
It is asking me about whether I might qualify for extra payments by receiving ESA income-related. from May 2012.
But surely, whether CR or IR, isn't the amount due the same?
They want to means test me by means of this form and I don't see how I would benefit,
Is there another motive for them trying to get more info. out of me?
Can you please clarify and advise what would happen if I did not send it back?

Thank you

A