You'll find a scroll wheel on many newer model and pricier mice today. The scroll wheel is controlled vertically, and usually located between the left and the right click buttons on a mouse. The scroll wheel allows you to maneuver up and down a page by simply moving the button with your finger. Instead of dragging your mouse to the scroll arrow on your screen to view more content, this feature saves time and energy. While gaming, the scroll wheel may allow you to switch weapons or perform some other task by rolling the wheel.
Cordless mice do exist and prove very handy to many people.
Some mice use infrared technology. This would require your mouse to be relatively close to your computer as a clear line of sight will always be required. Some mice also use RF technology, which does not require a clear line of sight between your mouse and your computer. Cordless mice work great at presentations or simply at home. Some of them can function while up to six feet away.