Macgilly, all three statements are true. Too much steam creates a flattened loaf with thick chewy crust with cuts that don't open. If over risen, less steam will allow the crust to set quickly, preventing the bread from flattening out. The right amount of steam allows slightly under risen bread to stay moist longer letting the bread rise more. The right amount of steam promotes a rich crust color and surface shine and also increases the volume of the bread.  In the early stages of baking, the rapid increase in enzymatic activity on the surface of the loaf breaks down the starches in the dough into simple sugars that contribute to crust coloring. For a detailed discussion of the role of steam in bread baking, see Bread, A Baker's Book of Techniques and Recipes, Hamelman, (Wiley).  

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