Fully realigning the IRS every flight is a company procedure; perhaps. For Boeing a 'fast realign' is enough, especially with GPS a/c. The B757 I assume had similar systems to B733 classics. We used to fast align on turn-rounds in Europe, but a full align before any ETOPS or long over water flight. On NG we sued to fast align on turn-rounds and full align on crew change because the a/c was shutdown, or it's nice to start with a clean sheet of paper if the crew are at the steps.