Story points are predictive. We want to reflect on those predictions to compare them against real data. Our goal is to provide metrics like "on average, it takes us X time to complete 8 story points."
To support this goal, we want to estimate in story points, but to log work completed in time.
we do our long range t-shirt size estimating in story points, but when we do sprint planning, we do capacity planning by hours or days. This brings a good discussion to the SP estimated issues with HOW it will be done and how long it will take. Depending on this answer, the team may decide to break the issue down further. It would be nice to still be able to do estimating by SP, then have a field for a time estimate - AND log work against these issues in time (hours/days)