For your home applying window film to your windows will keep prying eyes from looking into your home. We all have windows so we can look outside, and that remains the same. Passers by or neighbours can easily look into your home. This can be a security issue or just simply make you feel uncomfortable in your own home.
The less obvious benefit is that it can filter out harmful UV rays and prevents direct sunlight from coming into your home. The direct sunlight and UV rays do affect ageing and discolouration of furniture, paint and floors. By preventing the harmful sunlight, but still getting the warmth and light from natural sunlight you have a winning combination.
The film also adds to your security. The film used has a similar effect as the smash and grab film on your car windows. It will not prevent a person from breaking the window and entering, but is surely makes it more difficult.