When the player encounters an obstacle/enemy in Sonic the Hedgehog, the knockback that Sonic experiences provides A) a brief pause to play, where the reduction in momentum is given time to set in, B) pushes Sonic away from whatever last damaged him, and C) pushes Sonic away from the center of the dropped Rings, allowing the player the ability to pick up a fair number of them while still moving forward.

 The Sonic the Hedgehog Series Turns 23!

Sonic the Hedgehog is a video game franchise created by Yuji Naka, and is developed and owned by Sega. The first game titled “Sonic the Hedgehog, launched on June 23, 1991 for the Sega Genesis console after Sega requested a mascot character . 

The franchise centers on a series of speed-based platform games, but several are spin-offs in different genres. The protagonist of the series is an anthropomorphic blue hedgehog named Sonic, whose peaceful life is often interrupted by the series’s main antagonist, Doctor Eggman. Sonic usually must stop Eggman and foil any plans of world domination. [Wiki]