To my knowledge, at the time this was written, that procedure is up-to-date so it’s the recommended process to follow if you have multiple tenants in order to have different development environments and then one for production.
The tagging allow us to have more context about the purpose of each tenant/domain and also imposes some distinctions relevant to you. For example, non-production domains have different rate limits for Management API. In addition, I did a quick test and accessing the Tenants section on support center showed me all the tenants/domain under the selected subscription (in my case all my domains are under the free subscription).