[sgift]

> (...) but at some point you may find that your application has grown and your SQL server is running into IOPS and CPU limits that are difficult to fix.

It's not unique to SQL/databases that at some point your user base may outgrow your current architecture and you may have to invest in something else.

It's dangerous to think you can skip this and just employ whatever architecture is "good" for bigger user bases from the start. There are different trade-offs in different systems and the trade-offs of most alternatives are not as well understood as the trade-offs of databases. I have seen more than one project implode when something which was simple with a database was far more complicated with the alternative.