It's important because it stores the training exercises and the learning exercises into our more permanent memory while we're sleeping 7-8 hours in bed.
I scrubbed in on a 4-hour paraesophageal hernia last night, then i got laid, and now three ambulances are coming in full of bloody, broken car crash victims, all who need to be cut open.
So, the night before the test, go to sleep early, get a full eight hours of solid sleep, wake up early, do whatever you need to do in the morning, go to the test center relaxed.