Progressive cam profile acts like a small diameter reel at low throttle openings, and a more aggressive large reel at openings beyond 40-50%.
Sensitive control for small throttle openings for best feel, more aggressive at large openings for faster acceleration.
Good for many conditions, including low traction mud or sand, where initial throttle opening is sensitive for good feel. Reduced on-throttle "hit" of powerful motocross bikes for better control, but maintains an aggressive throttle feel at larger openings.