There is a no of scenarios where the field values are auto-populated on the field change of a sublist field. For example, when an item sublist field value has been set in the sales order item lines, then fields like rate, tax code, description, location, etc will be automatically populated in the item line.
The auto sourcing on-field change can be switched on or off using suiteScript in the sublist lines. if the ignoreFieldChange is true then auto sourcing can be switched off on the field change:
objRecord.setCurrentSublistValue({
sublistId: 'item',
fieldId: 'item',
value: true,
ignoreFieldChange: true
});
if the ignoreFieldChange is false, the outsourcing will be there on the sublist field change. ignoreFieldChange value is false on default.