The amount of Blight on the base board is roughly balanced with the Blight cards - your total Blight pool is smaller, but you have no negative effect. However, it is slightly easier to play with - first, because the certainty of knowing exactly what will happen makes some decisions easier / clearer / less risky; second, because with ongoing-effect Blight cards, there's an early-game pressure to not let the island go Blighted (as the earlier it happens, the worse it is), whereas with the base blight space it doesn't matter when Blight is placed, only whether it empties.
(The early-game pressure is also present with immediate-effect Blight cards and the Event deck from Branch & Claw, as some Events key off the island being Blighted.)
(Discussion elsewhere) Tags: Blight, Blighted Island