Natural light

The attraction is quality for free. A large window is a big soft source, exactly what expensive modifiers try to imitate, and skin under it looks right with no work at all. The cost is control: cloud cover changes your exposure mid-take, the sun moves across a long session so shots cut together badly, and you can only film while it is light. Sitting at roughly 45 degrees to the window, with a white wall bouncing back into the shadow side, is the standard setup.