What is the credential (pilgrim's passport)?
The credential is an official document that certifies and identifies the pilgrim. It shows his/her personal data, maps of the Pilgrim's Way and boxes where the stamps are entered in the places where the pilgrims pass through, and the date. This document is essential to stay in public hostels (albergues) and obtain the 'Compostela', but it does not give any other rights to its holder.
Nothing unnecessary just exactly what you need for your Camino