Why you ask?
Well, whilst I don't want to knock them, as polishes do have their time and place, I'll cut to the chase. If you have a brand new, well looked after car, even a restored collector car (that's a very broad term, covering past/present and future classics) with a new, original, or just with a fresh coat of paint, you don't need to use a polish. This is because the abrasives found in most polishes do a good job of what they are employed to do; strip off a fine layer of paint to expose a new layer underneath. Given that paint is on average between 50-150 microns thick (that makes a bee's look big, trust me), this should only be done as a last resort, if at all. Majority of the swirl marks you get in your paint are dutifully put there by the same abrasives as well. Another thing we don't think should be the result of using any car care product.
Polishes, along with most 'one step' miracle products ("Cleaner Wax" is just re-named polish) tend to either do one of their tasks well at the expense of the other, or do both poorly. The one step method that provides cleaning and protecting in one easy action, either builds residue up on itself or does not supply enough of a protective barrier, causing your paint to start going backwards, FAST. You naturally use more of the polish to gain back some of your shine but this works temporarily, before you lose your glow again. Before you can say 'Killer Shine', you're back in the auto store buying more polish.