vcds or not to vcds that is the question?

Fabia MKII 1.6TDI CR  REG 63  CAYA engine. The filter has only 2 pipes & is a sealed canister.

Over the last few days I have been looking at the best way to change my diesel fuel filter there seem to be 2 train of thought. always use VCDS or just fill the filter and crank it over.

My Question is

What exactly does the VCDS do when you have just changed the fuel filter?

Where does the air go when you turn on the VCDS?

How does the air get out of the hpfp?