Goblins and Drow would attack the Druid Grove at night to get a darkvision advantage.
Players would steal the Idol of Silvanus during the night when most Druids are asleep and to get a stealth advantage.
Those two events alone just seem wrong as daytime scenes.
Otherwise being able to explore during night time is just generally amazing for atmosphere. Selune and Shar are present in BG3. Darkness, Moon, Moonrise Towers, hello? =)
There are many shady things, and vampire things, that simply require a night time scene. The city of Baldur's Gate in BG1 comes alive on another level when you can walk the streets at night and the music and ambience changes. Add some criminals and thugs in the mix to make night time more dangerous. (note: I don't want to see level scaled level 10 Thugs in BG3 when we reach the city just to get a challenging encounter. But maybe if the PC is alone at night, you could be attacked by 5 level 2 Thugs. The party doesn't have to do everything together.)
