Chris Biscardi: A Stream Deck is a piece of hardware that basically has a set of keys that you can program to do whatever you want. You may have heard of things like AppleScript and other automation tools like Alfred and whatnot.
A Stream Deck is basically a keyboard that you can just program to do whatever you want, even if that thing is multiple actions.
For example, on my Stream Deck, I have a number of different buttons, one of which is a start button which will set up basically everything I need software-wise to get started streaming, and also send me live and send the tweet, and set up my starting scene.
I also have some more benign buttons, like a button to mute my mic whenever I need to. I don't need to go and find, dig through a bunch of software to mute my mic if I need to.
A bunch of my themes have muted mics on them already, so if I'm in a new scene, which I also have buttons on my Stream Deck to swap between scenes, then I don't need to worry about it. If something happens unexpectedly, it's super-nice to have that hardware button just sitting right in front of me.
There's a couple of other things, like flashback recording. If something cool happens on stream, I can hit a button, record the last five minutes, save it out to a file, deal with it later.
I have more advanced theme transitions, which will take basically a set of layers between two scenes, turn some of them off and on, wait until some of the animations are done, and then turn more sources on behind them.
This makes it nice to have very fluid theme-to-theme transitions. You don't need them, but if you have a Stream Deck, you can set up a sequence of steps that happen when you push a button. That makes them really nice.
You don't need the hardware to use a Stream Deck. There is an app for a Stream Deck that you can run on your phone. It does basically the same thing.
That's what a Stream Deck is. You don't, strictly speaking, need one, but they are useful if you are going to do streaming quite a bit.