The BOUNDARY command enables rapid creation of closed polyline areas which makes for easy hatching. Once the zone is hatched, it can be moved around and the hatching is pulled with it - a feature known as associative hatching.
The figure below shows a boundary area showing an area that will become a soakage pit. Once an area has been defined as a boundary, even though it has been hatched, the association between the boundary and the hatch pattern stays, making for easy editing.
Tip: Unlike the polyline command, the end entity snap settings stays operational while the BOUNDARY command is in operation.