As a man who has done amateur to intermediate speedruns in many games, I can attest to Pory's answer.
Legend of Zelda: Twilight Princess (Bare Minimum Completion)
World Record: 5:39:??
Personal Record: 8:24:16
Donkey Kong Country (102% Completion)
World Record: 00:50:00
Personal Record: 00:54:00
Super Mario Bros. (Bare Minimum Completion)
World Record: 00:05:17
Personal Record: 00:05:53
For a video game enthusiast like me, playing the game over and over is fun, but to be able to play a game at the absolute best of your abilities and see how you rank with the world champions... THAT is a truly rewarding experience.