I have never had mine in a "dark" place. It sits on my school room dresser in our "school room"/playroom, away from windows. The pro to having it in a darker area is you don't have to worry as much, (especially with styros)of the flunctuation of temps with the turning on/off of the room lights and the rising sun in the room having a bigger effect of room temp changes. And yes, those things do and will affect the temps, especially if you do not have a thermostat controlled bator, (which I don't).
With the better bators and better heat control, I really don't see where it would make a difference as to the actual light vs dark. I am an avid candler and my poor littles get light shined on them almost daily when I candle.....lol I have awesome hatch rates, highest being 100% (20/20), but average more around the 90%. I usually don't have more than a couple (local/my own eggs) that don't make it after lockdown. Even with the shipped eggs I did a couple months ago I had 14 make it to lockdown and 12 hatch.