A 100% stacked area chart is a variation that focuses on proportional representation over time. Each area is scaled so the total height of the stack is always 100%, making it possible to see how the relative contributions of each category evolve.
For example, it could be used to show how the percentage of users coming from different devices (mobile, tablet, desktop) has changed over a year. The total remains constant, emphasizing share of contribution rather than actual growth or decline.