Earlier this week Dawn commented on my "Rooster" post. She said, "how does that work with the eggs for eating, vs eggs for hatching?" This makes a nice blog post so here's the answer.
Until they begin an incubation process all eggs are for eating, even fertilized eggs are eaten. There are some who say fertilized eggs are more nutritious than non-fertilized but I have not found any research that says this for certain. Chickens who feel "broody" and want to incubate actually spend a week or more collecting a clutch of eggs. The eggs are kept dormant until she feels she has enough. She'll then sit on them nonstop for 21 days. Once she begins sitting on them you no longer want to eat them of course. If you collect eggs everyday you have no worries about grabbing an egg that has begun incubating.
I do have a desire to eventually have enough roosters (they recommend 1 for every 20 chickens) so that I can incubate them myself instead of purchasing chicks each year. My aunt does this. She collects eggs every spring. She'll do just as the chickens do, collect eggs for 7-10 days and then incubate. In 2006 she collected 300 eggs (she got some from neighbors as well) and usually hopes for about 50% hatch rate. This time she had over 200 eggs hatch!!! She does this for meat supply more than anything. She only keeps about 30 laying hens. She had lots of meat to share that year! I really want to do this eventually so I may need to purchase just some roosters because I don't think one rooster can keep up with 42 laying hens. :)