There's always been those who'll use a trackball in preference to a mouse or trackpad. Other than aesthetics there's very good reasons for this, not least that employing different controllers is an effective way to reduce risk of Repetitive Stress Injury (RSI) when using your Mac.
Easy to use; extra features beyond other trackballs; nice looking; can help prevent RSI when used in conjunction with other controllers
Action is high for RSI sufferers; accuracy in use doesn't match that of graphics tablets