In an ideal world, you'd...use it to ensure your baby gets the healthiest, least processed version of mashed carrots.
In reality...by the time most of us get the knack of this thing, the baby has moved on to more solid foods. While he is in the pureed foods phase, though, you can cook those carrots in boiling water or a steamer basket, and then use a fork to smash them. Not smooth enough for your tot? Add some of the cooking water and whip them together in a food processor or with an immersion blender until they're to his liking.