Subscribe by Email: How does this relate to New User Registration?

WP sends me emails for New User Registrations. All Registrations end up in my WP user database.

Q1: Do Subscribe by Emails end up in a different place than Registrations?

Q2: Do Subscribe by Emails also produce New User Registrations?

Q3: For Multi-site, must a user Subscribe by Email for each site of interest?

Q4: Is there any indication in the WP Users list that a user has also Subscribed by Email?