Error input item in work order include in planning flag Help me pls :'(

when trying to edit operation (assigned output item to input for the next operation), we have this below error :

'You must disable include in planning for the input item in operation 20 to Add item WIP_123 as an output item'

• Does anyone know what happens if we ignore the "include in planning " flag ? What are the effects in planning module if we enable the flag (since supplies and demand only recommend work definition)

(Context : recent update in manufacturing, we can have output item as inputs for the next operation, this is what we're trying to do)

We have supply and demand planning but we don't implement production scheduling