Take the following not so hypothetical situation:
- Project Lead create user story and adds estimate of 3 hours.
- Developers estimate per hours on tasks within user story totalling 6 hours.
Where’s that extra 3 hours come from? Who is accountable for the extra 3 hours the project lead or the developer?
Planning poker helps here but we don’t do it at the moment so we’re reliant on whoever is available at the time to create initial estimates that this isn’t going to happen.
All this assumes that we allow developers into the project planning stage (which we really should).
Another issue I can think of is that if we have a high estimate ticket of say 20 hours and something goes wrong the likelihood is that estimate will be blown out of the water, including risk as a factor in story point calculation should help with that.
Playing devils advocate though I can see how it’s difficult to equate story points != hours as when a project starts there is no gauge of initial velocity.
I think the above points are fairly weak but 140 characters isn’t enough for this kind of thing.