The benefits with a propeller polishing 
A general guideline from the IMO (International Maritime Organisation) states that new ships through available technology such as new types of paint will enable to achieve environmental improvements (less CO2 emissions) of between 12-23%, while existing ships can be 5 -12% more efficient through retrofit processes.
New technology and new types of paint supplemented with hull cleaning and propeller polishing will obviously increase these percent points.
In addition, if you polish the propeller blades with diamond disks in water then you will get a smoother surface than even the manufacturer can deliver.