Well, Poser 6 tries to automatically set the displacement bounds correctly, so unless you see obvious holes in the geometry at bucket edges, you don't have to worry about setting the bounds yourself. Other than that, in ordinary situations (like simple texture-driven displacement of an object in the center of your scene) will only barely impact your scene. Things will take longer if you have complex procedurals in your displacement shader, extremely large displacements or displacement in very very close-up situations. Displacing geometry over several buckets is more expensive than displacing things within one bucket, both memory- and calculationwise.