When handling large lists, what actually slows things down: the number of elements we render, or when we choose to load more?

Turns out, both . But they're separate problems that need separate tools. Virtual Scroll → manages how much is rendered at once. Intersection Observer → manages when work gets triggered Virtual Scroll keeps the DOM lean no matter how large the dataset grows. Intersection Observer watches the viewport and fires logic only when something actually comes into view. Which one has made a bigger difference in your projects?