What difference is there to eating fertile verses infertile.
The only significant difference is in the mind. There is no difference in nutrition, how long they will last if stored properly (keep them under the mid-70's so they don't develop. Non-fertile eggs stored too warm can go bad too from bacteria but they will not develop.), no difference in taste or consistency. The only difference in appearance is the bull's eye if you know what you are looking for and look real close. For some people that difference in the mind is important.
Why do big outfits candle the eggs before shipping
To avoid surprises to the customers. Most people getting eggs from the store would be horrified to find blood spots, meat spots, anything like that in their eggs. They would think there is something unsafe in them. Some of the blood spots and such can be prettty massive and unappetizing. The eggs that are identified as not being perfect in the candling are sold to bakeries and such, where the egg is mixed up and the defect is hidden.
what if ther is blood in egg whites.
I use it anyway. Other than looking unappetizing, it is not going to hurt you.