Use of the authentication token

Hello everyone,

I want to train an Image Classification model, and when I run the training script I am asked to enter an Authentication Token. I have read about it in other threads, but there is still a point that is not clear to me:

In the past I have trained other HuggingFace Models (For example, BERT, or GPT2 for NLP) and I was never asked for an authentication token.

Is the token required only for certain models? And which kind of models and why?

Many thanks in advance and have a nice day!