Extispicy was not a fringe practice consulted only in private anxiety, it was built into how Mesopotamian states actually made decisions. Royal archives, particularly from the Old Babylonian kingdom of Mari and from the Neo-Assyrian court, preserve extensive correspondence in which baru priests report their readings directly to the king before military campaigns, building projects and diplomatic decisions, and a negative or ambiguous liver could delay or cancel action a king had otherwise already resolved on. The baru priesthood constituted a recognised professional class with its own training, its own textual canon and, at the royal level, direct access to political power that few other kinds of priest possessed, since a king who ignored an unfavourable extispicy risked being seen by his own court as defying the gods' explicit answer rather than merely bad advice.
The practice also had to survive its own uncertainty. Because a single reading could be judged flawed, ambiguous, or contradicted by a second sacrifice, Mesopotamian diviners developed formal procedures for repeating an extispicy and for weighing conflicting results, a level of internal methodological self-scrutiny that modern historians of science and divination alike have found notable. Extispicy's prestige and its heavy documentation, resting on the sheer bulk of the omen literature it generated, made it the benchmark against which other Mesopotamian divinatory techniques, including astrology and the reading of unusual births, were measured for authority and reliability.