Most laptop comes with wifi card and ethernet port. Some time you will be connected to your internet via Wifi and other time using ethernet port. When you are connected to internet via ethernet it is a wise to disable your wifi card but doing it manually could be cumbersome task.
Here is excellent freeware utility BridgeChecker that can automatically disable/enable wireless interfaces. This conserves IP address allocation, reduces security risks, resolves dual interface routing issues, and prolongs battery life.