The CMOS is special memory where your BIOS settings are stored. The CMOS battery is a back-up power source when the PC is turned off. Removing this battery when the PC is off, results in the clearing of settings in this special memory (CMOS). Those settings will reverted back to default.
The reason you remove the battery for a extended period of time is due to the Motherboard & CMOS's ability to retain a charge. By waiting a period of time (10 seconds to whatever) you ensure that all electrical charges will be dissipated. Then the CMOS will no longer retain your saved settings - BIOS reverting back to default. The CMOS Clear Jumper is basically a CMOS battery Bypass. Change the PINS and the battery no longer powers the CMOS. The waiting period still applies.
"The only time you want to use "CMOS Battery removal or CMOS Clear" is when you have made changes to your BIOS's settings and are unable to boot or re-access your BIOS." i.e (Overclocking or incorrect settings)."