Ever had one of those days when you receive email from another programmer who didn't zip his files and as a result, you get left with Outlook saying:
"Outlook blocked access following potentially unsafe attachments ..."
There's a registry hack to get around this but why bother playing with the registry when someone or something else can do it for you?
It's free and it works really well. Even shows you a list of what those extensions are listed as to make it easier.
And it automatically restarts Outlook so your changes will take effect. (this was always a pain for me because even if you exit Outlook, if you use ActiveSync, it keeps running)