Where it genuinely matters
On tidal water the moon is the whole story. Spring tides around the new and full moon move more water, and moving water positions predators at ambush points.
Spawning calendars for many species also track lunar cycles, particularly in salt water.
Where it is overstated
On an inland lake, wind, front timing, and water temperature will each swing your day more than moon phase will.
The honest version
Use the moon to plan a tidal trip and to anticipate a spawn. Do not use it to explain a bad day on a reservoir.