Fats Melt
    Example: Butter melts when heated

Sugars Caramelize

    Example: If you brush milk on top of a pie crust and bake it, it browns or caramelizes    

Proteins Coagulate

    Example: eggs coagulate when cooked

Starches Thicken
    Example: gravy thickened with flour or corn starch thickens when cooked

These simple facts probably won't change your life, but when built upon additional baking knowledge, they may help you trouble shoots issues, understand how certain recipes work (ie how custard thickens), how to avoid simple mistakes, or help you to make something without a recipe.