Polishing blades was pre-requisite prior to a C of A test flight. It certainly works, and will never hurt your blades. Keeping you blades washed and cleaned is a basic maintenance action, that no only keeps them clean, but ensures the blades are receiving a continuous detailed inspection. A dirty aircraft and dirty blades are indicative of inferior maintenance and inspection.
The only person I can imagine suggesting that would suggest that you never polish blades is some workshy shirker who would rather surf the Internet than actually do any work!
