They could use the fief in exchange for military service. Hope this Helps!
The three social classes in ancient Sparta were: the Spartiates (free citizens with full rights), the helots (slave employed in production activities), perioeci (free citizens that wandered around, <em>"dwellers around",</em> who were mainly traders or craftmen).
Spartiates dedicated their lives fully to becoming high quality professional soldiers, as actually military activities which were the common objective of the whole society. Since they were children they were educated by the state-sponsored education system, the Agoge, that fostered values such as obedience, discipline, courage, loyalty to Sparta, self control, etc.
