99% of the people that do this have no understanding the reason behind it.
It was a way to get around vehicle tire width laws in the EU. It has been around since the late 80's.
2001 Focus ZX3 Race Car in Germany-Ours
2010 Renault Clio 1.2 16V in Germany-Hers
2004 SVTF EAP/ST170-Mine
2013 Focus ST2 TS NAV SUNROOF-Hers