I have a group that very frequently swaps different resources (e.g., developers) in and out of projects. This makes it difficult for PMs to maintain the resource task assignments due to all the changes. To resolve this, they would like to assign all tasks and any ETC only to roles. Then they would assign any named resources to the task with zero allocations and zero ETC - i.e., only so they could enter time. The result would be that ETC would only be assigned to roles, and all the actual hours would only come from the resources' time sheets. They would then zero out any ETC as tasks are consumed, and compare the role allocations to the resources' actual hours. What are the implications of this approach?