What is the ‘has list-id containing’ iCloud Mail rule?
a unique identifier for a mailing list regardless of the particular host that serves as the list processor at any given time.

https://tools.ietf.org/html/rfc2919
You can use this to perform an action for a specific mass email, such as a company's newsletter.
If you used the email address, that might change. list-id won't change.
You can find the list-id in the email header.