Imagine you work with your Raspberry Pi in the studio in your own network, then your router should give your Pi an IP address via DHCP, all is fine.

The big day comes and you take your Pi to the exhibition, stage, whatever and want to SSH in it with your shiny laptop. No DHCP no IP address so you have to prepare with a static one in the configuration on the PI. Usual documentations show an either or solution which is suboptimal for the mobile artist. How about giving a dynamic and static in the same configuration and forget about it? So the Raspberry takes a DHCP address dynamically and still is reachable under the static address. You could either make it happen in the dhclient.conf or in the /etc/network/interfaces where you add eth0:1 to your network, it gives a second ip address to your very same eth0 interface, the whole would look like that, at least for me on Raspberian distribution, I give the 10.10.10.10 IP but you can chose your own: