coconutWiFi displays you a small aqua-bubble at the top of your screen which indicates whether you're in range of a wireless network or not.
Imaging the following: You're on a trip with your iBook, PowerBook or MacBook Pro and you want to check E-Mails or do something in the internet.
So you're searching for a wireless access point. To do this the "normal" way you have to check the Apple airport-menu continuously to see if a network is in your range.
This normal way is very bad because of two facts:
1. You will miss many networks, because you don't want to open and close the airport-menu all the time
2. In the airport-menu you don't see if the network is encrypted or open - you have to try to connect to verify this