My .02 cents Chip...
The primary reason you would lift the buffer at all is to avoid cutting too much paint on an edge, when you're rolling over the end of a panel, say a hood etc. In other words;
Most right handed people will naturally focus the pressure of the buffer on the 12 o'clock to 5 o'clock area of the pad , since they're moving left to right in their passes (or should be). By lifting up slightly on the left side of the buffer as you approach that edge, you prevent cutting the paint down unevenly on the edges there when your right side is overlapping the edge, or "hanging 10" as I like to say. Remember; you don't want to run the buffer up TO the edge of a panel, but OVER it, because the outer edge of any pad is perhaps the most dangerous to that thin area of the paint.
Otherwise, you DO want to keep it flat as possible, and with as even - handed pressure applied as humanly possible. If you tilt in the middle of a panel, you'll risk getting buffer marks or holograms from the polish or compound, and just undermine what you're attempting to clean up.
If you keep a rotary moving, chances are you will NEVER burn or cut through the paint in the middle of a panel. However, if you aren't careful around the edges and ridges of a panel, and you don't "roll off" past the edges with a slight tilt on the left side of the buffer, you can remove enough paint there by the left side of the pad hitting /slapping that edge where the paint is naturally thinner. I always recommend a beginner TAPE OFF edges and ridges. Even pros do this, it's insurance. Even with the above technique, you would still need to protect the very edge because the middle of your buffing pad would be on top of it as you "roll off' the right side of the pad over the edge, and you'd see no paint left there afterwards. You can remove the(masking) tape prior to doing your your final pass or 2 to even and polish everything up uniformly.
Hope this makes sense.
