Different polishes have different cutting and filling properties.
For those of you interested, here's a list clicky (http://www.detailingworld.co.uk/attachment.php?attachmentid=109&d=1141047784) of the grades of the products that the more discerning detailers use.
You will need Winzip and Excel to load and see it.
Mods might want to put a sticky on it.