Two obvious reasons come to mind (unsure if these guys solve either) - 1 - Scalability. It's nice to have instant scale up/down 2 - Complex deployment - Herok

Two obvious reasons come to mind (unsure if these guys solve either) - 1 - Scalability. It's nice to have instant scale up/down 2 - Complex deployment - Heroku has proven that if you can make it dead simple to use git and spin up tons of databases/third party software, people will pay for it.