It depends on the area. I've ridden some great rides late at night in areas that were well lit and saw nobody.
But the area I live in now is more commercial, with a lot of bars and strip malls. During the day it's not too bad, but at night it can be a little scary. The kids are out, driving way too fast. One of my riding buddies got nailed at a 4 way stop last year when a kid blew the stop sign and took a right turn doing some drifting. Never saw my buddy until he nailed him. He stopped long enough to see my friend laying in the road and then he took off.
And from my bar band days, I can tell you that a high percentage of drivers late at night, and especially on weekends, are impaired. Some nights it seemed like almost every car was a drunk or a cop.
Obstacles also become a problem as they're much harder to see.
Az