Give WP-Cli User Home Directory Privileges

I am on an Ubuntu 18.04 local dev environment, running a WP Multisite 5.5.3

Three Part Question:

1.) What (who) is the WP-Cli user? And,

2.) How do I give that user permission to "my_user’s" home directory?

3.) Should I be worried from a security standpoint about giving the WP-Cli home directory access?