The electrically heated conductive coating on the outside of windows 1and 2 has the function defogging,and ice build up prevention. The conductive coating on the inside of windows 4,5 prevent fogging
The temperature controllers maintains windows 1, 2 at the correct temperature to ensure maximum strength in the event of a bird impact.
The MEL or QRH will direct you to adhere to the bird strike speed below FL 100with inop window heat. Some A/c, such as 757 have a lower limit e.g 313 kts below fl 80.
Boeing systems manual refers 3.20.2