Energy Efficiency
The first and most crucial point to consider when considering why windows are installed in homes is that they can have a significant impact on the energy efficiency of your home.
This feature will only be relevant in particular circumstances, but it is an important one to consider regardless.
To state the obvious, windows are composed of glass, which is a transparent substance that serves its purpose well. As opposed to obscuring or blocking light, glass allows light to enter a building from the outside environment; in most cases, this is sunshine.
During the chilly winter months, this can result in a significant increase in the efficiency of the treated air in your home. The sun's rays not only provide light, but they also provide heat; windows allow you to tap into this energy source and harness it to raise the temperature of your home without placing additional burden on your home's furnace.
However, as previously stated, this would only be applicable in the unique case of cooler temperatures in the environment.
During the hot summer months, there's a good probability that your windows will actually reduce the efficiency of your home, as those warm rays enter your home and the treated air that you're using to cool your home will be absorbed.

Lighting
You won't be able to get any sunshine into your home if you don't have any windows. However, by using a window, you will be able to acquire access to a more powerful source of lighting than you would otherwise have.
As a result, when it comes to the lighting of your home, windows are extremely important.
In some shape or manner, lighting is required in every home; it is the only way for us to be able to see well within a structure. Because without lighting, we'd all be fumbling around in the dark and knocking into each other and the furniture.
Without windows, you would be forced to rely solely on artificial lighting to brighten your space. We define artificial as anything that is not produced by the sun in terms of its functional meaning.
Most of the time, this refers to light emanating from either a light bulb or some other type of light fixture, depending on the situation. These also have a negative impact on the energy efficiency of your home because they require a significant amount of electrical power to operate.

Windows and Psychology
Our genetic makeup is predisposed to a desire for and enjoyment of sunlight. Windows make this possible, and as such, they are critical to the design of a well-planned home.
A large number of studies have been conducted to demonstrate the relationship between emotions and sunlight. After being denied the sun's warming rays for an extended period of time, humans become significantly less emotionally healthy and stable.
Due to the fact that sunlight is essential to our physical (thanks to all of the Vitamin D), as well as emotional wellbeing, there are conditions such as Seasonal Affective Disorder (SAD).
Windows play a significant role in our lives because they allow us to live in structures (which is necessary since we need to be sheltered from the weather and have a secure place to live) while still receiving and absorbing the sun's nourishing rays.
Remembering our imaginary home with no windows, you can quickly get a feeling of how dark and cramped it would feel.
However much artificial lighting you used, the house would still feel walled off, secluded, and oppressive. Windows are an important and necessary feature of every home, which is why you'll almost certainly never see a house without them!