Discussing about the effort required for each task/story, is crucial to generate alignment within a team, determine better the scope of a task/story -- and deco

Discussing about the effort required for each task/story, is crucial to generate alignment within a team, determine better the scope of a task/story -- and decompose it, if it appears that the effort would be so big that tracking what has been done and what remains to be done would be intractable. The by-product of these discussion may be summed up as a number. But oh yes its unit must not be time.