Making dynamic addition field/fieldset control is awesome features and user-friendly. Building web applications/CRM containing multi data enty fields, sometime required to add many field for additonal informations. In this case using this feature user can directly add/remove additional fields and enter data's without support by a programmer.
Example: In Job portals some candidate have less collage/graduation information but another case there might have many collage/many graduations. Dynamically add/remove fields will really helps for these kind of cases.
Find the below example for adding addition contact no fields.
Adding form fields dynamically
shanidkv
December 15, 2014