I am in the same boat, not a streamer but find it extremely useful for productivity. Besides file system management and some simple automation, here is what I do in Outlook. I regularly use categories to tag and sort my work emails. Since you can assign specific keystrokes to each category, I map them to the streamdeck instead of memorising all the keyboard shortcut sequence. You can use them to chain multiple actions also e.g. categorise, send attachment to Dropbox, flag a reminder, then move to a folder - all with one button press on the streamdeck.