Email Templates
Email Templates let a project define reusable, editable designs - the wrapping layout (header, footer, brand colors) that individual email templates render inside of - rather than hand-coding HTML for every outgoing email.
Designs
A design has a body template with placeholders that get interpolated at send time, plus a set of starter templates to build from. Creating, updating, and deleting a design all persist immediately and apply to every email template that references it.
Where designs are used
Transactional email - invitations, password resets, webhook email deliveries - is rendered through a project's chosen design, so updating the design updates the look of every one of those emails going forward.
Preview before publishing
Changes to a design can be previewed against its starter templates before being relied on for real sends.