The personal access token is optional but your request may fail if your repository has more than 20 branches.
Providing your personal access token increases the API rate limit to 5000 requests per hour, which should handle repos of all sizes.
See this doc page.

This doc will help with getting a personal access token.

You can set up a new personal access token here.
There is no need to include any additional permissions for a new token used here when presented the option.

We do NOT share or store your personal access token under any circumstances.
You can verify this by viewing the source code here.