When you change a title or add/remove new speakers, the Generate Virtual Sessions toggle will update your event as necessary and send new speaker emails as necessary. Newly added speakers will need to confirm in the email sent from ATIV and also only newly added speakers will receive emails from Zoom.
For critical changes like date or session time updates, the Generate Virtual Sessions toggle will make those updates as well. In this case though, it will first delete the original webinar or meeting and will then create a brand new meeting or webinar. All speakers for this webinar or meeting will receive new emails with new links and would need to confirm in the email sent from ATIV. Webinar panelists (speakers) will also receive a new email from Zoom.