
From a practical standpoint, it makes it almost impossible to actually see the lot. Since location is the hallmark of real estate, the lot the home is on is almost as important as the home itself. Additionally, it's sometimes difficult to access the property (see my icy driveway post).
As for the interior of the home...
If the Sellers were smart and left the home well lit:
You know how everyone looks hotter by candlelight? It softens the wrinkles and adds a glow to the skin and a sparkle to the eyes. That's what your getting with a warmly lit home. Cracks in the drywall, funky floors, dinged appliances - they'll all be softened by the glow of lamps. What is obvious under the glare of natural light can be missed at night. Also, you need to make sure the the home DOES get lots of natural light during the day.
If the Sellers (I'm looking at YOU Mr. Banker) have left the home dark:
Well, I probably don't have to go any further with this. If you can see it, you can't buy it. Duh.
My recommendation is this: you should always do a second showing on a property you're thinking of purchasing. If the first was done in the dark, make sure the second is in full daylight.
Oh, and never buy a car in the rain.