Water Soft Oil

What does adding egg or milk do to a basic bread recipe?
I’ve finally mastered the basic white bread recipe with yeast, flour, water and oil. It comes out as a soft yet chewy bread.
I see other recipes where an egg is added or milk is substituted for water. What does this do to the texture and firmness of the bread?
Thanks in advance.
Milk will add a richer flavour, and eggs will add a lighter, fluffier texture.
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