Currently, despite our best efforts, PMs from time to time will delete a task/issue that had actual hours logged to it. The system doesn't "delete" the hours, but reclassifies them as Project hours, instead of Task or Issue hours. However, this creates a problem for us with financial reports that we use where we are tracking cost centers and codes for accounting at the Task/Issue level.
In order for the reports to be correct, we have to recreate the issue/task that was deleted, re-assign the resources, add the hours back that were deleted, and then delete the Hours that were reclassified a Project Hours. Sometimes depending on how much time was logged this can be a nightmare to fix.
We have created a special view that showcases Tasks/Issues with hours and includes verbiage, "Actual Hours, Do NOT Delete", but it still happens. The recycle bin that is coming out will be a big help, but it would be nice if there was a setting at the Project Level or Group Admin Level that could be set to eliminate this from ever happening.