In our opinion, it is a very important part of incubating eggs, if you own an incubator then you should really have an egg candler, unless you have the ez-scope. The reasons are for this is one of enjoyment so you can actually watch the little chick developing inside the egg and i must be honest with you, this experience is not one easily forgotten. I am afraid the other reason is a serious one and that is to remove infertile eggs from the incubator, if you do not remove non-fertile eggs then the risk of bacteria growth in your incubator is very high and if this is able to get in fertile eggs through the pores then it may make the chicks too unwell to hatch or even kill them during incubation.
Ideally candling at 10 days for a novice should tell if fertile or not.