Submiting a form to join multiple groups should send one email, not one per group
https://docs.civicrm.org/user/en/latest/email/set-up/ says: "When users subscribe to multiple groups at once, a confirmation email is sent for each group separately."
This should be changed to send a single email. They entered their email address 1 time into 1 form, then get multiple emails that ask to confirm their email address. Some will think that it's unnecessary to click each link since their email address is confirmed by just clicking one. Some will think there is a bug in the system. It really just doesn't make sense to users.