Mechanical decontamination is the opposite of chemical decontamination. Whereas chemical decontamination removes contamination from a surface without any physical interaction, mechanical decontamination doesn’t require any chemicals and relies solely on physical interaction.
A polished car will stay cleaner for longer, and will in fact be much easier to clean, even without protection added. This is due to a surface that so smooth that dirt has less chance of getting caught in the microscopic hills and valleys.
When you have stone chips, you probably want to fix it. However, it is not like you can just spray paint your car again. Certain stone chips are more easy to repair then others. With a lot of practice, it can give a very good end result.