The distance that a lens is focused at, is where objects will appear the sharpest. And objects in front or behind that focused distance will gradually become more fuzzy or blurry as their fore/aft distance increases. You might want to use a large depth of field when taking group photos. You want enough depth of field to have everyone’s face in focus, especially when you have more than one row of people. You might want to use a less depth of field when taking it of something for example having the background blurred or if you want to emphasize an object in a photo, by making everything else less focused.
I am going to use this as a guideline for my Heather Edwards shoot as I could focus on raindrops and use it for when I do my lighting workshop (Imogen Cunningham) as I could focus on a certain part of the object I use so they stand out from the other parts.
