Im gonna turn this topic on its head a little and mention the MOST NECESSARY feature that was never implemented in one of my projects.
It was an iOS client for a medical records system. Since it contained actual confidential medical information, some patient records could be “restricted”. Thos meant if you tried to open them you would be prompted for a reason, and this would be audited.
We already had 2 different iOS apps with this feature in place matching the web app. But for some reason with the 3rd app they just decided not to bother. I discovered that it was because the PO in charge of that project didnt consider it important enough for the demo. So we have one app where you can just bypass the whole auditing process and open restricted patient records freely.