Understand delete row action in subform
The 'Delete' button is present in the subform and will allow the user to delete a new entry to the subform. The delete row action will allow you to execute certain actions when the 'Delete' button is clicked in the subform. Do note that only deluge scripts can be associated with the 'Delete' button.
Note: There are differences between the show/hide options that are available in the forms and the subforms. The show/hide option in the form focuses on whether to display a field present in a form. While the show/hide option in the subform focuses on whether to allow the user to add or delete new entries to the subform.