Originally Posted by cheezydemon3
............ Aren't most recipes assuming a full boil?
All of the recipes in Brewing Classic Styles
assume a full boil.
Most extract recipes from Northern Brewer assume a 20qt pot and top-off water, IIRC. I think AHBS asks you to get the largest pot you can find.
When you switch to full boils, aeration/oxygenation becomes increasingly important. Adding top-off water introduces plenty of fresh oxygen to the wort. Boiling drives it off.