Window cleaners typically avoid using soap because it leaves residue on the glass, leading to streaks and smudges. Instead, they opt for specialized window cleaning solutions formulated to evaporate quickly and leave a streak-free shine. Soap, particularly those designed for general cleaning purposes, tends to contain oils and additives that can leave behind a film on the glass surface, diminishing the clarity and cleanliness of the windows. Additionally, using soap requires more rinsing, which increases the likelihood of water spots and streaks forming. Therefore, professional window cleaners prefer to use specially formulated solutions or a mixture of water and vinegar to ensure pristine results without residue or streaking.