I have tried to use the introduced work log feature to log the work done on issues in order to build up some estimation history - but so far we have not succeded.
One of the challenges we have had is that the work log operates in calender days which are quite confusing - depicted by this example:
If I create an issue and we estimate it to last one day - we set the initial estimate to 1d. The developer works on the issue for one day and reports that he has used 8 hours (= one working day) - then Jira tells him that he still has 16 hours left of the estimated time.
I could ask the development team to report work logged by days - but then they have to remember to log a half days work as 12 hours.
This is confusing - I have locally worked on changing the Jira representation so 1w = 5d (workdays) and 1d = 8h (one working day) which definately looks nicer.

What I would suggest is a general preference so people can adjust hours/day days/week to make the work log work the way they prefer.