I probably candle a lot less than the majority of people who candle. I candle when setting eggs to make sure I'm not putting one in with a hairline fracture or a problem and then, it varies.....Usually I candle at day 10 and lockdown (day 18) and that's it. I've already done day 14 and 18 and once day 18 only. These were very dark eggs and I was afraid early on I would have trouble seeing anything. I've hatched white, colored,, brown and chocolate eggs and there are different visibilities.
If there is a problem with an egg, unless it is leaking, you can take it out later rather than sooner. I came to this conclusion after my first hatch when I would have, candling on the recommended schedule, thrown some away but since I realized I didn't know what I was doing I left them and every one hatched. So after that I've given the eggs the benefit of the doubt unless they really (really really really)look like quitters.
I know people say with a broody they move them around, knock them about and aren't as careful but I have a better hatch rate than my hens. They're around 50 - 66%. I'm close to 100%. (My eggs only. Shipped eggs are a whole different story.)
So especially if you have some eggs you're really hoping to hatch, less may be better in the candling department.