Because the systems almost always employ some type of clutch mechanism, a build up of heat and wear will result from continuous use. (mechanics.stackexchange.com)
If I am not mistaken the 2001 Yamaha Diversion has a clutch cable and does not have a hydraulic self adjusting clutch mechanism. (mechanics.stackexchange.com)
In Engine Drive mode, which only kicks in under heavy load conditions / high speeds (100 - 120kmph and above), the motor directly powers the front wheels through a lock - up clutch mechanism. (cardekho.com)