What does preseed file accomplish?

Hi,
I'm building a custom .iso to add some educational features to kali. Still haven't gotten the build to successfully complete but jumping ahead to the "Mastering section", I see information on preseeding. Could someone explain this to me?
I'm not sure if we would want it or not.
Kim

0x05 – Add a preseed file that will run through a default Kali installation with no input (unattended). We can include a ready made preseed configuration and alter it as needed:

mkdir -p config/debian-installer
wget https://raw.githubusercontent.com/of...tended.preseed -O config/debian-installer/preseed.cfg