This is only really necessary in the case you don't want DHCP. If you are dealing with an encrypted LUKS server on the internet, you will often want to have a static IP so you know which IP to connect to (or if you have a semi-static IP assigned by DHCP).
SET IP Address by /etc/initramfs-tools/initramfs.conf
IP Address=192.168.1.27
Gateway=192.168.1.1
Subnet Mask: 255.255.255.0
Hostname=myhome.com
IP=192.1........