This is a great technique that has recently been introduced to a number of cameras. It allows the photographer the ability to shoot a range of images while the camera automatically racks the focus of the lens and then combines these images into a single image.
This is particularly useful for macro or flower photography where a significant Depth of field can be achieved while combining the relatively blurred background of say an F2.8 on a 100mm macro lens. Ideally this technique would be used on a tripod, however many quality lenses and cameras have IBIS or Image Stabilisation which really cuts down the need to a tripod significantly. Stacking an array of images at 2.8 can offer the same depth of field of say f16, the same sharpness as f2.8 but the same background as f2.8.
Another use of focus stacking is with landscape photography where a very deep depth of field is required with a modern high megapixel camera. While this can often be achieved using a tint aperture such as f22, diffraction is becoming a significant issue with the newer High megapixel cameras. Many start to see diffraction softness creeping into images at only f8. So this technique allows a multiple images taken with a larger aperture and then combined into a single image which resolves high levels of detail while retaining the deeper depth of field of say f22.
I’ll be covering this technique (and more) in my next upcoming one day “flowers workshop”