Project manager is a role. People within projects may have different roles, for instance a particular person can have the project manager role as well as the lead architect role.
This principle is rather important especially when human resource and/or financial planning needs to be performed. For instance, the hourly rate of a project manager might be different compared to that of a lead architect. You can also monitor more easily the hours spent by the different roles which could have different budgets.
Management also means delegating and monitoring what’s going on rather than performing as much ...