benefit to having !bbox! query manually placed inside subselect beside other WHERE?

mapnik_pg_test.sql

/* (SELECT * FROM polygons9 WHERE iucn_category_id = 2) AS GEOM */

tiledb=# explain analyze SELECT AsBinary("the_geom") AS geom from
(SELECT * FROM polygons9 WHERE iucn_category_id = 2) AS GEOM 
WHERE "the_geom" && SetSRID('BOX3D(-20037510 2505758.018505042,60267.60323439911 8276874.507094959)'::box3d, 900913);
                                                                                                                    QUERY PLAN                                                                                                                    
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on polygons9  (cost=19.85..264.07 rows=8 width=93117) (actual time=1.173..2.883 rows=21 loops=1)
   Recheck Cond: (the_geom && '010300002031BF0D00010000000500000000000060F81B73C18B5F5E020F1E434100000060F81B73C16A3E74A0E2925F41003AB24D736DED406A3E74A0E2925F41003AB24D736DED408B5F5E020F1E434100000060F81B73C18B5F5E020F1E4341'::geometry)
   Filter: (iucn_category_id = 2)
   ->  Bitmap Index Scan on polygons9_gist_idx  (cost=0.00..19.85 rows=480 width=0) (actual time=0.306..0.306 rows=350 loops=1)
         Index Cond: (the_geom && '010300002031BF0D00010000000500000000000060F81B73C18B5F5E020F1E434100000060F81B73C16A3E74A0E2925F41003AB24D736DED406A3E74A0E2925F41003AB24D736DED408B5F5E020F1E434100000060F81B73C18B5F5E020F1E4341'::geometry)
 Total runtime: 2.923 ms
(6 rows)



/* (SELECT * FROM polygons9 WHERE the_geom && !bbox! and iucn_category_id = 2) AS GEOM */ 

tiledb=# explain analyze SELECT AsBinary("the_geom") AS geom from 
(SELECT * FROM polygons9 WHERE the_geom && SetSRID('BOX3D(-20037510 2505758.018505042,60267.60323439911 8276874.507094959)'::box3d, 900913) and iucn_category_id = 2) AS GEOM                                                                                         ;
                                                                                                                    QUERY PLAN                                                                                                                    
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on polygons9  (cost=19.85..264.07 rows=8 width=93117) (actual time=0.410..1.971 rows=21 loops=1)
   Recheck Cond: (the_geom && '010300002031BF0D00010000000500000000000060F81B73C18B5F5E020F1E434100000060F81B73C16A3E74A0E2925F41003AB24D736DED406A3E74A0E2925F41003AB24D736DED408B5F5E020F1E434100000060F81B73C18B5F5E020F1E4341'::geometry)
   Filter: (iucn_category_id = 2)
   ->  Bitmap Index Scan on polygons9_gist_idx  (cost=0.00..19.85 rows=480 width=0) (actual time=0.305..0.305 rows=350 loops=1)
         Index Cond: (the_geom && '010300002031BF0D00010000000500000000000060F81B73C18B5F5E020F1E434100000060F81B73C16A3E74A0E2925F41003AB24D736DED406A3E74A0E2925F41003AB24D736DED408B5F5E020F1E434100000060F81B73C18B5F5E020F1E4341'::geometry)
 Total runtime: 2.012 ms
(6 rows)