Location: Automatic, is just a Network Location setup for DHCP, which means it just gets its IP address, network mask, router address, and DNS server addresses from the local DHCP server.
In your situation, if one location is always ethernet, and the other location is aways WiFi, then you could create a location where the Airport interface obtained it IP address via DHCP, and the ethernet interface used a fixed IP address, assuming that was your goal.
But if you are WiFi at both locations, or both locations are ethernet that would not work.
Personally, at home I use the same fixed IP address assigned to both my WiFi and Ethernet interfaces with ethernet being set higher in the food chain. If at home I'm transferring a large file, and decide I need a faster interface, I just walk my MacBook over to the ethernet switch, and plug in an ethernet cable. The MacBook automagically switches over to the faster gigabit ethernet interface without loosing anything on the in-progress file copy. I can unplug the ethernet cable and it will automatically switch back to WiFi. This is because I'm using the same IP address on both ethernet and WiFi interfaces so the copy operation which is at a higher layer in the TCP/IP stack does not notice the change in low level interface. If I had different IP addresses, then my file transfer would break when I switched interfaces.
