If you simply connect the switch to the router, it will run with a default configuration. That hardly makes sense, you could have bought a much simpler and cheaper switch.
I run the controller software on a Windows PC. With it I can configure the Ubiquiti devices, view statistics, etc. If the controller software is not active, the switch continues to run exactly the same. There is only a gap in the statistics.

You don't necessarily need Unify Cloud Key Device. You can also download the software with the controller for Windows or other... But you should make sure that the device incl. software is always running... I myself have decided for Cloud Key Gen2 incl. HDD...