Caching happens at several levels: the browser saves files so return visits load instantly, the server saves generated pages, and a CDN saves copies near users. Each layer removes repeated work, cutting both load time and server cost.
The main challenge is knowing when to refresh the cache so people don't see stale content. Good caching balances speed against freshness, serving cached copies for as long as they're still accurate and updating them when the underlying content changes.
Updated July 2026