Dave:
Yes, exactly! A resource always needs to be allocated to a project (i.e. be a team member of that project) in order to book time for that project.
Thanks for the education.
Tried to understand that by opening a case in 2004 and only now do I see the light until now.
Being able to add unassigned tasks or no is a system setting with the options varying if different versions of Clarity. It has nothing to do with rights.
While allocating resources to a project is booking and requires booking rights and cannot be substituted or overridden with any setting.
It is to be noted that the functionality of adding unassigned task as Dave points out is limited to those projects into which the resource is already booked.
The booking functionality is outside the timesheets and time entry process.
That is even if the user has booking rights (eg is the resource manager) while adding tasks to the timesheet of another other resource he cannot book the resource to a new project through the timesheets.
That is only the projects where the resource is already in the team are available and it is not possible to add projects that are not already there. (The booking must be done where it is normally done.