Ask HN: What do you think about software estimation?

Some people like developers to estimate in story points based on complexity, some on estimated number of days.

Managers or whoever asks for things to be estimated wants to establish team velocity so they get to know how long things take and how to plan accordingly.

What do people think of 'estimations' especially faced with developer uncertainty and the potential overhead associated with the 'act' of estimating things you haven't even started on