The 1/3 rule applies well: If you are only using the server one third of the time then AWS is a good deal. That could mean 8 hours per day or 10 days per mont

The 1/3 rule applies well: If you are only using the server one third of the time then AWS is a good deal. That could mean 8 hours per day or 10 days per month or 4 months per year. In those cases AWS/public cloud is more efficient and convenient than buying servers, but there are additional exceptions. Certain applications with lower uptime requirements (test environments) can be run on decommissioned older prod server hardware if you have that. Legacy enterprise applications that rely on extremely fast database access with large relational databases and poor caching are better suited to bare metal DB servers than virtual servers of any kind (public or private).