The summon monster spell chain is useful, but it's challenging to players and Dungeon Masters alike because it summons a lot of different creatures, applying the celestial or fiendish templates many of them. The Augment Summoning feat from the Core Rules additionally modifies the summoned creature's Strength and Constitution scores, which changes its hit points, Fortitude save, and usually its grapple modifier, attack and damage modifiers, and skill check modifiers as well.