Just what illusions actually used smoke and mirrors?
Smoke is used in all sorts of things, where you want to obscure something for a moment, or create a dramatic distraction. It won’t often be key to the actual mechanics of a trick, but it’s a big part of the stagecraft.
Mirrors are most often used in a vanishing box. Picture a box with a square cross section, with a mirror along the diagonal. The audience can see the open front of the box. The top of the box is also open, though this may or may not be visible to the audience. From the front, the audience sees the solid bottom of the box, and also sees a mirror image of the bottom of the box where the back of the box should be. This portion the audience sees is empty, and thus the entire box appears to be empty, but there’s still half the box’s volume available behind the mirror to hide things in.
I always think of the classic ‘smoke and mirrors’ trick as being like the one James Franco used at the end of Oz The Great and Powerful, where you project an image onto a cloud of smoke thus making it much larger and giving it a ghostly and ethereal appearance.