We plan projects based on workdays only. However, there are some items that track things like off-site operations, travel, or shipment, which are tracked in calendar days. We have the option of setting this on a per-task basis, however when viewing tables or Gantt charts, there is no clear way to distinguish for any given task whether its duration is tracked in calendar or work days.
Some visual way to quickly tell these apart, e.g. showing them in different colors or columns, would be extremely useful to avoid confusion when presenting schedules and doing roll-ups.