How does egg effect to bread?

Try it sometime. It will affect the liquid amount you will need so just decrease that a bit. The loaf may rise a bit higher and be a  little fluffier.

If you use just the egg white,you can get the same effect but it may tend to dry out faster. The lecithin and fat in the yolk enrish and actually help preserve it,as any oil would.

The best way to see how ingredients affect a loaf is to use a familiar,simple recipe (french bread) and add the ingredient to a few batches. See what you consistently notice. Any "failure" is usually still very delicious.

Have delicious fun!