Good question - specifically Horizon Cloud Service on Microsoft Azure requires the 'Contributor' role attached to the Application registration (Service principle) for the correct operations to be performed.
The reasons for this are that;
1. the automatic deployment of the environment will create networks and subnets along with adding VM's and configuring network security groups (NSGs)
2. once the environment is built, then ongoing management of desktop/application assignments (e.g. RDSH Farms) requires VM's to be life-cycle managed (created, powered on/off, deleted)
3. if you need to delete the node for any reason then the deletion will remove vms subnets etc if they are not in use. (to do this go to Settings->Capacity , then select Node-->Node Details ---> Delete)
As such, these require the contributor role to do so.
This is covered in more detail in the Pre-Requisites document and the Getting Started Guide.
both linked in the VMware docs portal (VMware Horizon Cloud Service Documentation) and also in the Overview of this community.
Hope this helps,
thanks. this helps