[tabletopneedle]

With DH both public keys have effect on the randomness of the shared secret. If the app on the client generates a random DH key-pair for every session, and it uses a public DH value of the server pinned to it, the encryption is authenticated and secure to use.

If there are no public keys pinned to clients (say secure messaging apps like Signal where each user generates their own keys), users need to check the public key fingerprints to make sure there's no MITM attack taking place.

[lvh]

The public key fingerprints that need checking are important because they get introduced in 3DH, which is an AKE. Like 'tptacek mentioned.