Just got through polishing the deck on one of my boats. There was a thread on this board a few weeks ago and the consensus was (NO) I've been doing it for years and I use what ever Automotive polish is on sale. Polish is a super fine abrasive, wax and a solvent. When it comes time to re-varn, you're going to sand anyhow so use anything you want. What I like is that it not only shines, it removes mud and algea, scum etc that is actually on there because hosing off the boat doesn't remove all of it.

And believe it or not, varn is soft and always being sand blasted by particles in the air. This is why plastic windows are not used on homes by archectural standards.

I believe polish is a good thing on varnish!