Yes, that's true, but for apps with significant memory footprint I don't think it's a huge help. Heroku dynos have 512mb ram (https://devcenter.heroku.com/articles/dynos), so for an app that has a 200mb footprint you're looking at probably 2 worker processes. I'd still prefer for an idle dyno to handle a new incoming request, rather than remaining idle while an in-use dyno attempts to service two requests.