In most cases Multi tenancy would be overkill, except where there were legal reasons for distinct separation e.g. there will be sensitive info in Tenancy A that people in Tenancy B must never have access to including the Global Admins of Tenancy B.
Note, early on you could not have Environments in your Tenancy that were from different regions - and different regions may not include all the available functionality that is in the US region - and the article is an old article that has had some updates made to it and may still have some now 'legacy' reasoning.
You may also have fun if you needed multiple instances of other Azure/Office 365 products such as multiple Exchange online instances
Also, you may find some of the Capacity Limits are at the Tenancy level e..g. API Calls by a non-licence users (e.g. non-interactive).