Agitators do help certain washing machines clean better. An agitator is used to get clothes to rub together, which does a more effective job of removing many types of stains.
Agitators also cause more wear and tear on clothing. The rubbing action of the agitator can cause fabric to tangle and stretch in some cases. Using a washing machine without an agitator is an option when washing delicate clothes. Those types of machines also have more space to wash larger items, such as blankets and pillows. However, without the rubbing action, some types of clothing may need to be washed twice to ensure stains are fully removed.