AMP — Google's ultra-fast mobile pages tech.
What it does
Restricted HTML/CSS/JS — page in 0.3-0.5 sec.
Before (2015-2020)
AMP required for Top Stories carousel.
Now (2021+)
After Page Experience update — not required. Core Web Vitals matter instead.
When useful
News sites, AdSense publishers, slow sites.
Downsides
JS restrictions, analytics/ads limitations, double maintenance.