Whenever possible, clear an entire panel. We recommend stepping out your clear and clearing the entire panel on your last coat, or last two coats if you plan to polish. Why not just clear the entire panel with all coats of clear? The reason is that clear has UV screeners that affect the way light reflects off the panel.
Color as we know it is a reflection of available light, so when you blend the color back on a panel and carry it to the end of the panel, you end up with extra coats of clear on that panel compared with the adjacent panel.
For example: If you are painting a door which is adjacent to a fender, both panels had 2.5 mils clear from the factory. When you repaint the door, you reapply about 1 mil per coat. So 3 coats of new clear, plus 2.5 factory, minus .5 mil for wet sanding to prep = 5 mils on the door and 2.5 on the fender.
On a light color, this can result in a color mismatch. Even though you stopped the color well before the fender, it will still cause a color match problem due to twice the amount of UV-protecting clear on the door.