What three benefits do IPv6 extension headers provide?

Efficiency (headers only as big as needed), flexibility (add new headers for new features), and smooth incremental rollout (routers ignore extension headers they don't understand).

• Efficient: a basic packet carries only the 40-byte base header; you add extension headers only when a feature is needed, so you don't pay for unused options
• Flexible: brand-new features can be introduced as new extension header types without redesigning the base header
• Incremental / future-proof: you can deploy a new header in a test environment, and routers that don't recognise it simply pass it along — they don't break

Tip: This is the design lesson — by moving optionality out of the fixed header, IPv6 can evolve without a forklift upgrade of the whole internet.

Go deeper:

• RFC 8200 §4 — IPv6 Extension Headers — the chaining model that gives efficiency, flexibility and forward compatibility.