If you develop client applications, very often you come across an operation which is taking long to complete. Basically, you have 2 options; You can either do nothing about it, let the application "freeze" and let user wait for end of the operation. The problem is that the user doesn't know what is happening so he will become frustrated ("Damn, this app is really slow...") and may even eventually kill the application from the task manager, thanks to the "feature" of Windows which will mark the window as "Not Responding" and will offer the user an option to end the process.

That is why asynchronous processing (aka. processing in background) comes in place. The idea is that you display a dialogue to the user that informs him/her that there is something going on and that it may take some time to complete; or you can even let the user work with the application and literally do all the processing in the background.

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