We’ve made some tweaks to the site domains UI. It should now be more obvious that changes to the domains are queued in a batch and only applied to the server when you click the Save button. As you add, update, and delete domains, no changes are made to the server until you click the Save button. This allows you to make many changes quickly and process them in one batch, minimizing Nginx reloads and SSL certificate regeneration and downtime.
For more details, check out the Managing Site Domains doc.