I'm guessing they said that because Heroku doesn't let you save files to their system. You have to use something like s3. Other than that, I see no reason why s

I'm guessing they said that because Heroku doesn't let you save files to their system. You have to use something like s3. Other than that, I see no reason why someone would say that. You can save things to the tmp directory for a little while. The files should last long enough to do some work on them. For example, I've had an app parse an uploaded XML file that gets saved in tmp. This might not be a good practice, but I don't feel like setting up anything special for that app.