When an empty result is rolled, that means nothing of note has occurred from the rolls during that watch.

Doesn't roll to remove 50% of non-exploratory encounters when at a slow pace.
Doesn't remove exploratory encounters when the party is resting or otherwise stationary.
Doesn't roll for when oppressive conditions end.
Doesn't roll for veer.
Doesn't roll for procedural encounter faction allegiance.

Pace = What travel pace the party is travelling at.
Terrain = What terrain the party is moving through.
Styx = If the party is travelling on/following the River Styx.