Cleaning the windows of high-rise buildings is dangerous and slow when done by people on platforms or ropes. Robotic cleaners that climb or are lowered down a facade wash the glass automatically, keeping workers off the most hazardous positions.
Taking people out of high, exposed work is the main benefit, along with being able to clean large, regular facades consistently. The machines handle flat, uniform surfaces best and still need human help with complex shapes, obstacles and setup, so they are most useful on modern towers where the glass is extensive and the risk to human cleaners is greatest.