Very distant systems, i.e. extra-gallactic, like quasars, are used for the most accurate coordinate systems (e.g. the International Celestial Reference System/Frame, ICRS/ICRF3, the Gaia Celestial Reference Frame, Gaia–CRF3), because their angular velocities are negligible due to the huge distances where they are located.

Basing an inertial coordinate system on the observed positions of the bodies belonging to the Solar System is affected by much greater errors caused by the imperfect modeling of their relatively fast movements.

Using stars that are outside the Solar System is much better, but using distant extra-gallactic objects is even better.

If we did not have the "fixed" stars as a background on which to view the movements of the Sun, Moon and planets, who knows how many centuries later physics and technology would have reached the current level, because when seeing only the relative motions of the planets, without a fixed reference system, those are much harder to understand.

For interplanetary navigation, receiving signals from pulsars can be used as a backup or a replacement for atomic clocks. Individual pulsars, especially when young, are sometimes affected by "glitches" when their moment of inertia, thus the frequency of their signal, changes, but if multiple old pulsars are monitored, any glitches should be detectable and they should not affect operation.

Even the primitive humans of many thousands or tens of thousands of years ago knew to predict seasons by observing the rising stars and to navigate with the help of star gazing.

For the ancient civilizations dependent on agriculture, observing the stars, e.g. to determine when to sow various cultivated plants, could have a life and death impact, not a minor influence upon their life.