I’ve checked the documentation, but I don’t exactly have clarification on this point, since the explanation is spread across a few different articles.

I’m trying to make comments work a little better for my org, and I’m looking into using User fields to auto-set comment watchers. Based on the docs, I understand that “Notify users with base access when they’re added” means they’ll be automatically watching the record for incoming comments, but the language of that sentence is a little unclear. I’m afraid to turn on the setting for fear 200+ people are about to get hundreds of emails. Some questions about how this setting works:

• Do only users with base access get notified? Are interface users not included?
• Is the implication that adding a user to that field gives them base access? (Almost certainly a no, but the sentence can be read that way.)
• What does “notify” mean in this case? Are users notified by email when they’re initially added to the record, or are they just added as comment watchers? I already have an automation system set for these records that send to these users on record creation/update, and an extra “You’ve been added to this record” email would not be helpful or welcome.
• A lot of these User fields are actually Lookups fields of a User field in a common phonebook table. Lookup fields don’t include the User field settings. If the User field from a linked record has “Notify base users” set, is that user notified if that  User field is used as a Lookup in another table?