It seems there is always something new to learn in photography.  AF MicroAdjustments were an interesting one for me.  The story goes that I bought an f/1.4 50mm lens which wide open virtually sees in the dark.  When you get that wide, your depth of field is rather narrow and if your focus is off just by a hair, it shows.  Most smaller apertures give you a little leeway, but at f/1.4 you are down to the smallest movement that can throw you off.  So small that it’s even difficult to do it manually through the viewfinder so Autofocus is really important.  So I learned to adjust it for my 1.4 lens.