It is noticed that there are two new columns in the FIN_COST_PLAN_DETAILS table. These are PARENT_DETAIL_ID and DESCRIPTION. It is also noticed that these columns do not have any data in them.
Latest version tested: 16.2.2
These two columns are used for the Add Multiple Lines for the Same Grouping Attribute Values functionality. This is a functionality available only in the Modern UX. If only the Classic UI is being used, then no data would be present against these two columns.
There is also a flag called "Disable child row creation for Cost Plan Details" at Administration -> General Settings -> System Options -> New User Experience section. If this option is set to 'True', then "Create Detail Row" option would not be visible in the Modern UX.