There isn't a "right" answer to this. Some candle all their eggs and mark air cells on each egg. I think it is important for beginner hatchers to candle and learn what they are looking at. To recognize if the egg is developing normal or not. If random spot check candling works for you, I would compare those air cells to what is shown in the hatching 101 article, and adjust humidity accordingly. I mostly enjoy the goats, and the kids are lots of fun.