Before auto-layout, Figma components were static. A button was a fixed-width rectangle with text on top. Changing the label meant manually resizing the container. Auto-layout changed this by introducing the same model that frontend developers use: a parent that knows how to arrange its children, with rules for direction, spacing, padding, and sizing behaviour.
The real shift auto-layout introduced was not technical but conceptual. It forced designers to think in systems rather than compositions. A component built with auto-layout has rules — it behaves. A frame without auto-layout is just a picture. The discipline of building "behaviourally correct" components in Figma directly reduces the gap between design and engineering.
Nested auto-layout is where the power compounds. A button is auto-layout. A button group is auto-layout. A toolbar containing button groups is auto-layout. Each layer inherits and extends the logic of the one below it, creating compositions that are genuinely responsive within the design tool — not just in the browser.