This depends on the amount of memory a Puma setup would use vs an equivalent Unicorn setup. Say you have determined you need e.g 10 Unicorn workers, each taking 300 MB. If you could handle the same traffic using 1 Puma process with 10 threads that means you just saved yourself ~2.7 GB of RAM.

It's entirely possible that a single Puma process may end up using more memory than a single Unicorn process, so the only way to know for certain is to measure the difference.