EndInvoke. You should know that calling EndInoke is not optional, if you don't call it there will be some sort of memory leak. Even if you don't need to know when you method finished executing, and even if there are no output parameters and return value parameters you need analyse, its a good idea to call Endinvoke. Don't forget that you will not know about exceptions if you don't call EndInvoke... so just call it...
I know my fire and forget example may seem like its optional, but its not.
I will also update my article to include this information.
More information http://www.interact-sw.co.uk/iangblog/2005/05/16/endinvokerequired