Any reason to turn off wifi when connected by cable to network on A/C power for MBPr
Turning Wi-Fi off ensures traffic isn't accidentally sent over Wi-Fi instead of Ethernet. You can set the network priority in System Preferences, but I've had OS X send traffic over Wi-Fi even though it should have been sent over Ethernet. That being said, if you don't particularly care which network your traffic goes over, there's no harm in leaving Wi-Fi on.