What is the main purpose of the device management feature?

It adds a further layer of security.
Since you can choose individually which remote device - may it be a mobile phone or a remote desktop client - is allowed to connect to your project.
This is especially useful if the devices get lost or stolen, since you can revoke access with a single mouse click.

Furthermore you can specify which device class shall be used making it possible to provide panels the exactly fit to that device.