Cloudfront doesn't replicate your keys out to each edge each time you invalidate. It only retrieves them from the origin as a result of a cache miss. If TTL was

Cloudfront doesn't replicate your keys out to each edge each time you invalidate. It only retrieves them from the origin as a result of a cache miss. If TTL was 0 you would miss each request, making each request slower than serving directly from the origin.