Adding the extract late in the boil will keep it from darkening and caramelizing. It also can increase hop utilization, as the wort will be less concentrated during the majority of the boil. IMO the main reason to add late is to keep the beer color on the lighter side.
Draft 1: Lightly smoked Weizen
Draft 2: Belgian Wit
Draft 3: Rauchbier
Primary 1: German Scwarzbier
On Deck: Belgian Brown Ale, Pale Ale, Stout