Its a personal choice . So far what I have read about useing cartons sounds like alot of people have good results from it but you dont have to do it . Its like the humidity thing or what not everyone seems to have there own opinions on .
I use egg cartons that I have cut down by almost half and with a whole cut in the bottom, I tilt the eggs just a hair in them the big eggs that dosnt work for . Im new so Take it for what its worth so far this is what my eggs look like.
2 washed cracked eggs set in cartons, one clear one hatched
14 eggs washed and local put in egg cartons, all developed but at day 18 I didnt see movement in one. Its day 19 now so Im on the 2 day wait.
24 shipped eggs , many with bad air cells. a couple blood rings a few clears and one or two that may have started and stoped but looked funny the whole time. 10 babies alive and bouncey and one egg thats a wierd olive green color I cant see in worth nothing but it dosnt stink. These eggs came from NH to OR when it was very cold.
12 local eggs from a kids 4 H chickens so far at day 7 only 5 were growing most look unfertel and clear.
6 sizzle eggs shipped from a good distance away on day 4, all had disloged air cells 3 have possible viens 2 had diefent viens and a embryo and one nothing so far.
Dont know if that was annoying or helpfull good luck.