Why were the helots important to Sparta society?

Answer 1

They were serfs (farmers bound to the land who paid a percentage of their crops to their master) on the land which Sparta had conquered and taken from. Each Spartan citizen was allocated seven helots to work his plot of this land, and this freed the Spartan to concentrate on matters military and physical fitness.

When Sparta sent out an expeditionary force, each warrior took seven helots along to be employed carrying loads and used as light infantry and archers. This had the additional effect of reducing the number of helots left at home to reduce the possibility of a helot uprising, which the Spartans were always mindful of.

Later on helots were used to bolster up the declining numbers of Spartan heavy infantry, and if successful were offered freedom from serfdom as an incentive.