It's easy to google gory details on gyroscopic precession and Coriolis force and analyze every minute factor, but when (and if) is it worth doing?
Case study: standard army issue Fass 90 assault rifle, 300 m battle zero. How does it behave when shooting at an angle?
The Swiss army manual responds with exactly one concise sentence: "when shooting at an angle beyond ±30º, aim low". Not much for a mountainous country.