Its not about low latency but memory consumption too. If you have unlimited money to throw at Fly.io or AWS its no issue sure, but other than that you might wanna be mindful with the resources you waste due to using the wrong tool for the problem.

If your app goes viral for some reason and has to scale within hours its not easy to rebuild for performance in that timeframe. Then if u use stuff like AWS and your app has a shit payment model that allows free tier users to just waste resources, good luck paying off that invoice.