I may be misunderstanding what you mean but heroku does not spin up or down any processes, the amount of workers you have is controlled entirely by the end user and you will be billed by the worker regardless of how much traffic you're getting. I'd venture that 95% of heroku apps have a single process, and that 95% of the time those workers are in some sort of suspended state.
If you have 1 dyno, heroku spins that dyno down after 20-30 minutes of inactivity.
Also, there are services out there that will monitor your queue depth and increase your dyno count for you. Or, you could use the heroku gem to do that yourself.
