Updated programs serve at least three purposes:
a) Payment: How else would one record performance status if not by way of an updated schedule?
b) The planned v/s achieved progress at regular intervals. Even when the contract may not be specifically asking for it, contractors are usually required to present periodic progress status. Without knowing if performance needs to improve, targets may be missed.
c) Continuing from (b), a historic record of status is extremely relevant in claims (extension of time).
Updated schedules are also relevant in other ways, e.g. help in identifying and analyzing trends (a particular type of task may be taking longer than originally planned which can be identified and corrective action be figured out and applied); tracking KPIs, etc.