It's hard to overestimate the importance of having a good logging facility when you develop distributed applications. Did the client's request reached the server-side component? What did the server send back? Add to this inability of using debuggers while processing GUI events like focus change, and you may need to spend hours if not days trying to spot some sophisticated errors. That's why a commercial-grade logger is a must if you work with an application that is spread over the network and is written in different languages such as Adobe Flex and Java.