Extra-turn effects give a player another complete turn after the current one. That additional turn includes another untap, upkeep, draw, main phase, combat phase, and end step, making even one extra turn a substantial advantage.
Capture of Jingzhou provides another straightforward version of the effect, while Expropriate can potentially award multiple extra turns in multiplayer. Lighthouse Chronologist can eventually create extra turns repeatedly once it reaches its highest level.
