Sam's thinking was honestly pretty much in the same practical vein as Jessa's: it'd be easier to see stuff with more light. Although, really it depended where you were. The city never really got dark, not true dark, so the full moon would have less impact there, than, say, the middle of the countryside with no nearby source of light pollution. Although the city lights would be less focused than the moon's, which gave her the idea for an answer.

"Is it to do with the contrast of the dark sky on the water and light of the moon catching on it's ripples making it clearer to read?"

Worth a try, at least.