Summoned Creatures

Summoned creatures in Dungeon Siege can be a very effective way of augmenting your party's damage dealing capabilities.

On the other hand none of them are powerful enough to replace a character.

Unlike the necromancer from Diablo II, the summoned creatures in Dungeon Siege won't take out swaths of enemies quickly. You are limited to one, and typically it will only be around to absorb damage and cause a distraction rather than to deal damage or defeat enemies.

That said, I recommend finding one that is solid at melee. Getting something in the face of the enemy is a better option than having one that tries to maintain distance and shoot. They simply won't do enough damage to be effective, whereas every point of damage they absorb is a point of damage you don't have to heal later.

Leave the killing to your fighters, archers, and combat spells. Keep a pet around to take hits while you get better position.