Before and After: Why I use off-camera flash
Slide the vertical bar back and forth in the images below to see the difference between all ambient light and off-camera flash + post processing.
When shooting ambient light only, window views are often overexposed while adjacent rooms can look like dark caves. Adding off-camera flash balances the extremes and can help viewers get a feel for the flow of a home. In addition to allowing lighting of adjacent spaces, taking the flash off the camera helps avoid harsh shadows as well as overly bright foregrounds.
Shooting with interior lights on can introduce strange color casts as the camera's sensor produces a white balance for either daylight or the incandescent, fluorescent or LED bulbs. Again, adding off-camera flash takes care of the problem while also bringing the window view into correct exposure.