Tidal forces required in early evolution
The main argument for the need of a moon that I recall coming across is that tidal forces and flows provide a significant advantage to multicellular organisms over single celled organisms. Being long allows an organism to gain more movement and nutrients from the tidal flows, compared to a single cell creature.
This would create an evolutionary pressure to the more complex life form (which otherwise at this stage would likely fall prey to consumption by the existing simpler single celled lifeforms)
The outcome that has been discussed then is that without a large moon, would you get to multicellular lifeforms? If so what would be the pressure to do so?