was once told that at least one major airline, operating in a DME rich environment, did 1 full align first flight and then left it in NAV all day.
Yup.
SaudiArabian, with their TriStar aircraft did so, only switching the IRU's off with a tech crew change.
Litton IRU's feeding Hamilton Sundstrand FMS/FMC's...with a moving map (12 inch diagonal) included.
Superbly accurate....circa 1977.
Litton recommended that the IRU's remain in NAV rather than switching off at each intermediate stop to enhance MTBF rates.
Did this work?
Yup, sure did.