Re-racks are not necessary, but are commonly used in these occasions:

Re-Rack
If playing with 10 cups:» Cups are re-racked (reshuffled) at 6 cups, and placed into a triangle (3 back, 2 middle, 1 front)
» Cups are re-racked at 4 cups, and placed into a diamond (1 back, 2 middle, 1 front)
» Cups are re-racked (reshuffled) at 3 cups, and placed into a triangle (3 back, 2 middle, 1 front)
» Cups are re-racked (reshuffled) at 2 cups, and placed into a straight line (1 back, 1 front)
» Cups are re-racked (reshuffled) at 1 cups, and placed into the middle of the table (3 back, 2 middle, 1 front)
If playing with 6 cups:» Cups are re-racked at 4 cups, and placed into a diamond (1 back, 2 middle, 1 front)
» Cups are re-racked (reshuffled) at 3 cups, and placed into a triangle (3 back, 2 middle, 1 front)
» Cups are re-racked (reshuffled) at 2 cups, and placed into a straight line (1 back, 1 front)
» Cups are re-racked (reshuffled) at 1 cups, and placed into the middle of the table (3 back, 2 middle, 1 front)