With a basement additional storage and living space is created - extra bedroom, children's playroom, bathroom, gym, home cinema. Therefore the value of the house can increase significantly. A basement is an eco friendly, and often the cost effective, solution to gain more space on the same footprint where a plot is restricted by storey height and footprint.
A basement is an ideal solution for a hillside/sloping site. Plenty of natural light can be gained by using sunken patios and light wells achieving quality lower ground floor living with every basement.
Where poor soil conditions exist and expensive foundations, such as pile foundations, are being considered, a basement can provide a cost effective solution by providing not only the foundations for the house but also an additional floor.