We need the ability set Date-Time fields to Now (or %%CURRENTDATETIME%%) and perform other functions on them, using a Business Rule. For example I might want to calculate Now + 24 hours, or such and save that into a date-time field.
I have successfully tested using a Business Rule to copy the Updated On field to a custom date-time field. However, this is insufficient for many workflows. For example, an approval does not update the Updated On field, so capturing Updated On at this point will not result in the Approval Date-Time, but rather the time it was submitted for approval.