Why is the Scan-Mode important?

The Scan-Mode provides information on how many single LEDs are played by an IC. The mode is quoted in fractions. It means e.g. that with a ½ scan one IC controls two LED lamps, and with a ¼ scan four LEDs are played by an IC. With an increasing number of LEDs that are played by an IC, the brightness of the LEDs decreases. By using more expensive ICs, higher clock rates and lower scan-modes are realizable.