Say you have an XBox in your basement, the wireless router is on the first/second floor, and you wanted to use your XBox online without having a cable go downstairs. What you can do is get a laptop, bridge the wireless and wired connection. So then you can plug your XBox into your laptop and the computer will be acting as a bridge to convert the wireless signal into wired.
Thats just one example where I bridged two connections together.