Code splitting and lazy boundaries

Ship the code for this screen, not every screen

A dynamic import becomes a separate chunk that is fetched only when the code is first needed. Routes are the natural boundary; the second-best is anything behind a rare interaction, like an editor or a chart library inside a modal.

Every boundary needs a fallback, and the fallback should reserve the space the real component will occupy or you have traded a slow load for a layout shift.

Over-splitting has its own cost. Dozens of tiny chunks mean dozens of requests and a waterfall of dependent loads, which is often slower than one reasonably sized bundle.