Much advise I see/hear says to leave eggs alone once incubation is started, whether by hen or incubator. Why do you, if you do, candle them?? Seriously !!!!
I think some people just like to watch the development, but from what I've read, if you have an egg that's a dud and you don't remove it, it can explode and the rotten stuff can permeate the other eggs and kill the ones that ARE developing. A good broody (again, from what I've read) will push eggs out of the nest that aren't developing, so the exploding thing isn't an issue. I'm only planning on candling once or twice when I incubate this week.