Well... To be realistic, while there is generally no change in flow at night, reefs are regularly affected by a change in tides, which are about 5 to 7 hours different from eachother, so while the oceans current isn't truly afflicted by the position of the sun, there is an increase and decrease of movement in approximately 3 hour increments.
Every day, i manage to find an excuse to put my hands in my tank, so the breakup of flow while i am at home and the house is quiet (kids are asleep) makes a great time to make adjustments to coral that have fallen over, etc.
Reef threads podcast occasionally touches on flow, and go back and forth with experts on the benefits.
High, constant flow: stony corals grow firmer, stronger, and longer skeletal structures
Slow, intermittent flow: zooxanthelle algaes proliferate, and colors establish better; softer corals/zoas/palys grow with greater deliberation.