Use Case:  Multiline additional field sizes cannot be modified directly in the UI.  These can be modified using Field and Form Rules.

Execution Steps: 

1.  Create a new 'Multi Line' additional field and copy the "column name" of the additional field created from the additional field listview.

2.  Go to Admin > Incident Templates > Select a particular template > Include this additional field in the template > Field and Form Rules > Rule execution - On Create / Edit > Event - "On Form Load"  > Actions - Execute Script - Copy Paste the below code snippet and save the script.

var additionalField="WorkOrder_Fields_UDF_CHAR15";

var height=5;

var width="width:150%!important";

jQuery('[name="'+additionalField+'"]').attr('rows',height).attr("style",width); 

3.  Replace "WorkOrder_Fields_UDF_CHAR15" with the copied "column name" of the additional field.

4.  The request additional field will size will be modified in the new request creation form.

Field And Form Rule: