A lawn irrigation system is more effective if you are watering a lawn that is 500 sqare feet or larger. This is because hand watering is very time consuming and very unproductive. If you are watering a small area, such as trees, plants, and shrubbery, hand watering these items is much more effective as it is important to control the amount of water these plants are receiving. Additionally, it is useless to water these plants with a sprinkler if the water ends up on the plant rather than in the soil.