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
Subnet Mask: 255.255.255.0
Why won't my Linux Mint boot after I manually installed a new kernel?
apt-get install linux-image-newerone
dpkg -l|grep linux-image|grep extra
ii linux-image-extra-3.16.0-38-generic 3.16.0-38.52~14.04.1&nb........