Because sometimes it's a small task with a small time estimate that balloons out of proportion. You look sillier when your one day task balloons to five days, rather than your 10 day bundle of tasks balloons to 15, because a third-party library is poorly document and doesn't do what it claims to do in your specific context. Splitting the tasks doesn't make then go by faster.

I'm guessing the negative comment refers to "communicate this detailed hourly plan with your total estimate"

Providing an hourly schedule for a project as short as a week sounds completely crazy to me. Imagine how to pull that off for a month+ project. Maybe the sentence was phrased poorly.