Intended purpose of notmuch backend?

[eterps]

What is the intended purpose of the notmuch backend?

Is the idea that you can sync from imap to a notmuch backend directly? (so that notmuch does not need to be installed/configured on your system?)

An email client like aerc can use a notmuch backend directly, it seems you would not need a Maildir at all in that case.
But neverest does not seem to create a notmuch DB, and notmuch itself still depends on a Maildir being present.

Sorry if this is rather obvious, but I have trouble seeing the big picture.