Horizon cloud on Azure

I was just going through the video RDSH image preparation video in Horizon Cloud on Azure.  It's  mentioned after downloading the Windows 2012 R2 /Windows 2016 Datacenter editon from Azure Market it joins to the domain does the bootstrap  automatically after downloading the Daas Agent. 

Question:-

I think n Soft layer it's recommended that Image shouldn't be join to domain.  Is that some thing different here? 

Thanks

Venky