Cdfmxtech: I think what you're referring to is the IRS (or INS) in the ATT (attitude) mode. This is a degraded mode as you said supplying pitch/roll and heading as initially input by the crew.
As the inertial systems have matured, it seems like knob twisters like myself have less choices to choose from. Used to have OFF, STANDBY, ALIGN, NAV and ATT. Then we had OFF, ALIGN, NAV, ATT. Then OFF, NAV, ATT. The MD11 has OFF and NAV and I was told by a United mech that the IRU's aren't even switched off now on the 777.
You're only as good as your last departure.