Tenants usage

Hi
could someone explain the reasonable usage of tenants in SAP IoTs CF?

The root sees seems everything, created in all tenants. Everything (created by root, except the Devices and their Sensors, can be seen in all tenants by all users. If the tenant non-root administrator creates Sensor Type of Capability, it is visible only in tenant, until the root uses it for some device/sensor type (for example, Capability in Sensor Type), then it is visible across all tenants for all users...

Moreover, the user can have only one tenant assigned to...

I do not understand the reasons of all this. Or the tenant and its users are intended to separate Devices and their Sensors? And Root user can created tenant-independent devices?

Thanks in advance