danenania parent
Right, but if your goal is to have a lot of users (and minimal downtime), there's no point in putting a big avoidable obstacle in your path when the alternative is just as easy.
If your goal is to serve billions of users you should probably use cassandra etc. Why limit yourself to postgres if your goal is to have a billion users online at the same time?
Because cassandra isn't easy to set up and has all kinds of tradeoffs on consistency, transactions, et al compared to an SQL db.
On the other side, why not just store everything in memory and flush to a local json file if you won't have any users? sqlite is overkill!