The option Members of the share will see new shared emails in their inbox controls the following:
- If the option is not ticked (off), then shared emails are only added to the label that you are sharing, and do not appear in the Gmail inbox as unread.
- If the option is enabled, shared emails would also start appearing in the inbox as incoming emails (along with being added to the label).
If this option is enabled then when you share an email by applying a shared label on it, then other members of the share will see that shared email also in their inbox and marked as unread.
If this option is disabled, then emails are only added to the label that you are sharing, and do not appear in the Gmail inbox as unread.