There’s a great reddit thread going with the Onion’s Tech team on their recent transition to Django and this gem is buried in the conversation
And the biggest performance boost of all: caching 404s and sending Cache-Control headers to the CDN on 404. Upwards of 66% of our server time is spent on serving 404s from spiders crawling invalid urls and from urls that exist out in the wild from 6-10 years ago. [Edit: We dropped our outgoing bandwidth by about 66% and our load average on our web server cluster by about 50% after implementing that change]
Amazing result for such a simple change. Bang for your buck optimizations are always the best ones.