For now, the Dynamics 365 licensed users could only be added as a resource on Project Service.
However, there are many chances that we would like to assign a user who is not necessarily a user of Dynamics 365 as a resource for our project. It takes a lot of time and it is very inconvenient.

As a mitigation, we put a Dynamics 365 license on every user and add them as resources on Project Service. Then take the license away from those who do not use Dynamics 365 so that the users still remain as resources on Project Service and still be able to set in a project or so.

It would be more useful and give more flexibility to the use of Project Service if we could simply have a choice to add a user both Dynamics 365 licensed and non-licensed as a resource, as not all resources in a project are the Dynamics 365 users.