I assume it also have to do with evaporation rates in order to achieve the correct volume of wort at the desired gravity. Flavor development is another reason, from concentration & mallard (sp?) reactions.
Drive off DMS precursors...although you probably don't need all 60 minutes for modern base malts (except maybe pilsner). Sanitation should be taken care of in the first second of boiling. It's also helpful as mentioned for having enough water to mash and sparge and still be able to hit your volume.