The question is like asking "why do I need an operating system"? Or why live in a society with government services and laws instead of living alone off the lan

The question is like asking "why do I need an operating system"? Or why live in a society with government services and laws instead of living alone off the land? Databases are most valuable when there's more than one user at the same time, doing UN-anticipated things, involving multiple resources, whose uses may conflict with each other. Databases provide certain services that allow things to run smoothly as concurrency, amount of data, types of data, and unanticipated usage begins to scale up. In exchange, databases impose a tax that includes extra complexity, increased latency, reduced throughput, potential license fees and general bother. For coders who are just beginning a project, who are short of time and don't feel comfortable with a database, I see no good reason to insist on immediate database use. If their project scales to many users, a lot of data, and lots of unanticipated queries WITHOUT using any kind of database, the coders would have made a HUGELY interesting discovery - at least as interesting as map-reduce.