On the Planned Task table, several dictionary overrides exist for duration type fields where attribute is updated with 'max_unit=hours'. Those fields are, Planned Effort(effort), Actual Effort(work_effort) and Remaining Effort(remaining_effort).
The attribute 'max_unit=hours' ensures that the values displayed for these durations only display in Hours. (If the attribute did not exist, then those fields would display values in Days, Hours, Minutes and Seconds.
This attribute is not required and was only created for Project-specific tables to allow easier comprehension of durations on form.