In my experience, people don't estimate granularly because they want to be fast. They see this activity as a chore, an overhead, and want to get it over with qu

In my experience, people don't estimate granularly because they want to be fast. They see this activity as a chore, an overhead, and want to get it over with quickly. And planning sessions do take a lot of time even if we minimize the time it takes to come up with estimates. Sometimes, inaccurate estimates come back to bite us. So I regularly make the point that spending time on this chore is a necessary evil.