There's been a lot of discussion about this issue among Zaino users. Some folks want to go with their own observations, while others rely on the Zaino instructions. (After all, we certainly hope/trust that they have done even more sophisticated testing than most of us can!)
So ... the instructions and rationale, straight from the Zaino website:
From
http://www.zainobros.com/files/application.htm "Squirt a dime size dab of polish on your applicator and rub it into your paint using circular hand motions. Then, go over the same area using a straight back and forth motion on top panels and an up and down motion on side panels. Allow the polish to haze over (20 minutes is sufficient)."
My distributor explained to me that the circular motion is to ensure good spread of the product, then the straight-line motions are to let the "optical properties" of Zaino do their thing.
From
http://www.zainobros.com/files/tips.htm "Want an even higher level of optical light refraction and reflectivety. Here's how. When applying Show Car Polish do the following; On all Top surfaces of vehicle, use a back and forth motion (from front bumper towards windshield). On all Side surfaces (doors, fenders, etc.) use a vertical motion, up and down. This technique will increase the way light attracts and reflects off of Show Car Polish. The body lines and contours of your vehicle will seem to glow. This trick really works."
All I know is: I use the Zaino-recommended technique, and the finish on my white Jaguar (with about 7 layers of Z2 this season) has amazing depth and "wetness."
I do not believe the application method has anything to do with swirls or scratches. No matter what technique you use, you can get swirls and scratches.