I'm a candle-holic. I just finished my first hatch ever which, imho, was very successful. The ones that died early, I feel, were due to the fact that they were shipped eggs. Of the bad eggs, I had many that had broken air cells.
Many. The ones that were incubated for 3-5 days, I learned quickly which died early or never developed. A few blood rings were noted right away. I marked a question mark on all questionable eggs and placed them far away from my good eggs in the incubator...just in case they decided to explode.
Of those very early eggs, I had one quitter. The rest that remained as blood rings, I cracked, verified my findings, then moved on. When it came to lockdown, I candled a couple of eggs and right away I figured that since I had been candling regularly, that it would be impossible for me to even attempt to see through all these very filled looking eggs. The only problem was, I randomly candled eggs. I couldn't remember from one day to the next which one I had candled and which one I had not.
Lockdown day-Of the first 7 eggs I had placed in the bator, 4 did not make it. Apparently, 3 of them died before I even placed them into the bator. The 4th is questionable atm, but still alive. I verified this today when I cracked them open.
IMO, you can learn tons by candling regularly. Even more so by cracking open eggs that you candle and know are bad. You can't learn anything if you don't keep an eye on things.
BTW-the second group of eggs I placed into the bator 48 hours after the first was a huge success! Out of 8, seven made it out. The 8th one had pipped the wrong end a day early. I had randomly candled all of these eggs since about day 3.
Basically, I say....candle away! Make it quick and make sure you have steady hands so you don't drop any!